feat(Send Email Node): Add support for sending text and html email simultaneously

[pemontto]

V1 allowed populating both html and text properties. The V2 node introduced a mutually exclusive selection between the two.

This PR adds back the ability to send both HTML and text in the email so it can degrade gracefully.

Snippet of resulting email body with both types:

----_NmP-27aec6e9cf4b8f1e-Part_1
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit

Text Email Body
----_NmP-27aec6e9cf4b8f1e-Part_1
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: 7bit

<meta http-equiv="Content-Type" content="text/html; charset=utf-8"><b>HTML EMAIL BODY<b>
----_NmP-27aec6e9cf4b8f1e-Part_1--

Test Workflow

Click to expand JSON workflow...

{
  "nodes": [
    {
      "parameters": {},
      "id": "9d81ba9f-d7de-4d4d-986d-fd643a8cfda4",
      "name": "When clicking \"Execute Workflow\"",
      "type": "n8n-nodes-base.manualTrigger",
      "typeVersion": 1,
      "position": [
        280,
        580
      ]
    },
    {
      "parameters": {
        "fromEmail": "={{ $json.from }}",
        "toEmail": "={{ $json.to }}",
        "subject": "Test Email with HTML Body",
        "emailFormat": "html",
        "html": "=<b>HTML EMAIL BODY<b>",
        "options": {}
      },
      "id": "077a9963-72d0-4a90-8854-124869d7f3f7",
      "name": "Send HTML Email",
      "type": "n8n-nodes-base.emailSend",
      "typeVersion": 2,
      "position": [
        820,
        380
      ],
      "credentials": {
        "smtp": {
          "id": "2lCvKJhBMThyRcqJ",
          "name": "SMTP account"
        }
      }
    },
    {
      "parameters": {
        "fromEmail": "={{ $json.from }}",
        "toEmail": "={{ $json.to }}",
        "subject": "Test Email with Text Body",
        "text": "Text Email Body",
        "options": {}
      },
      "id": "fa6a26dc-725c-4af2-b212-a7f61e982365",
      "name": "Send Text Email",
      "type": "n8n-nodes-base.emailSend",
      "typeVersion": 2,
      "position": [
        820,
        580
      ],
      "credentials": {
        "smtp": {
          "id": "2lCvKJhBMThyRcqJ",
          "name": "SMTP account"
        }
      }
    },
    {
      "parameters": {
        "fromEmail": "={{ $json.from }}",
        "toEmail": "={{ $json.to }}",
        "subject": "Test Email with HTML and Text Body",
        "emailFormat": "both",
        "text": "Text Email Body",
        "html": "<b>HTML EMAIL BODY<b>",
        "options": {}
      },
      "id": "70d5ef42-f525-41f4-a7aa-4d73c074cfc3",
      "name": "Send Email with Both",
      "type": "n8n-nodes-base.emailSend",
      "typeVersion": 2,
      "position": [
        820,
        780
      ],
      "credentials": {
        "smtp": {
          "id": "2lCvKJhBMThyRcqJ",
          "name": "SMTP account"
        }
      }
    },
    {
      "parameters": {
        "values": {
          "string": [
            {
              "name": "from",
              "value": "user1@example.com"
            },
            {
              "name": "to",
              "value": "user2@example.com"
            }
          ]
        },
        "options": {}
      },
      "id": "f02a2373-e8fc-4f93-8d97-2eba56565b66",
      "name": "Set",
      "type": "n8n-nodes-base.set",
      "typeVersion": 2,
      "position": [
        500,
        580
      ]
    }
  ],
  "connections": {
    "When clicking \"Execute Workflow\"": {
      "main": [
        [
          {
            "node": "Set",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Set": {
      "main": [
        [
          {
            "node": "Send HTML Email",
            "type": "main",
            "index": 0
          },
          {
            "node": "Send Text Email",
            "type": "main",
            "index": 0
          },
          {
            "node": "Send Email with Both",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  }
}

[github-actions]

Great PR! Please pay attention to the following items before merging:

Files matching packages/**:

• If fixing bug, added test to cover scenario.
• If addressing forum or Github issue, added link to description.

Files matching packages/**/*.ts:

• Added unit tests to cover new or updated functionality.

Files matching packages/nodes-base/nodes/**:

• Added workflow tests for nodes if possible.

Make sure to check off this list before asking for review.

[codecov]

Codecov Report

Patch coverage: 9.37% and project coverage change: -0.01% ⚠️

Comparison is base (b6a00fe) 25.13% compared to head (a4042e9) 25.12%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6978      +/-   ##
==========================================
- Coverage   25.13%   25.12%   -0.01%     
==========================================
  Files        3150     3150              
  Lines      192105   192163      +58     
  Branches    21159    21169      +10     
==========================================
- Hits        48288    48284       -4     
- Misses     142835   142897      +62     
  Partials      982      982              

Files Changed	Coverage Δ
packages/cli/src/constants.ts	100.00% <ø> (ø)
.../MessageEventBusWriter/MessageEventBusLogWriter.ts	54.36% <0.00%> (-3.92%)	⬇️
...geEventBusWriter/MessageEventBusLogWriterWorker.ts	0.00% <0.00%> (ø)
...es/nodes-base/nodes/EmailSend/v2/send.operation.ts	0.00% <0.00%> (ø)
...ase/nodes/Google/Sheet/GoogleSheetsTrigger.node.ts	0.00% <0.00%> (ø)
...li/src/eventbus/MessageEventBus/MessageEventBus.ts	47.80% <13.04%> (-4.05%)	⬇️
packages/cli/src/CredentialsHelper.ts	25.35% <22.22%> (-0.14%)	⬇️
packages/cli/src/utils.ts	66.66% <50.00%> (-0.78%)	⬇️

... and 3 files with indirect coverage changes

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[janober]

Got released with n8n@1.4.1