[NEW] Add REST API endpoints channels.setCustomFields and groups.setCustomFields

[xbolshe]

@RocketChat/core

This PR extends #9424 and allows to change customFields for groups and channels.

Example:

POST http://192.168.2.71:3000/api/v1/channels.setCustomFields HTTP/1.1
X-Auth-Token: VvkuDTSlHxgL35_-Rd6LRSxAbVrcz-rPc_IddyI6C9U
X-User-Id: 3WpJQkDHhrWPBvXuW
Content-Type: application/json
Content-Length: 70
Host: 192.168.2.71:3000
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.1.1 (java 1.5)

{ "customFields":{"organization": "tra-la-la"}, "roomId": "GENERAL" }

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
X-Instance-ID: CEwWwBHqth7mjGYck
Cache-Control: no-store
Pragma: no-cache
content-type: application/json
Vary: Accept-Encoding
Date: Thu, 15 Feb 2018 18:48:04 GMT
Connection: keep-alive
Transfer-Encoding: chunked

{"channel":{"_id":"GENERAL","ts":"2018-01-21T20:58:41.142Z","t":"c","name":"general","msgs":45,"default":true,"_updatedAt":"2018-02-15T18:48:04.809Z","lm":"2018-02-11T11:52:16.836Z","topic":{"a":"b"},"customFields":{"organization":"tra-la-la"}},"success":true,"developerWarning":"[WARNING]: The \"usernames\" field has been removed for performance reasons. Please use the \"*.members\" endpoint to get a list of members/users in a room."}

POST http://192.168.2.71:3000/api/v1/groups.setCustomFields HTTP/1.1
X-Auth-Token: VvkuDTSlHxgL35_-Rd6LRSxAbVrcz-rPc_IddyI6C9U
X-User-Id: 3WpJQkDHhrWPBvXuW
Content-Type: application/json
Content-Length: 80
Host: 192.168.2.71:3000
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.1.1 (java 1.5)

{ "customFields": {"company": "sell-and-more"}, "roomId": "yJHQRaDFrakdggzAM" }

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
X-Instance-ID: CEwWwBHqth7mjGYck
Cache-Control: no-store
Pragma: no-cache
content-type: application/json
Vary: Accept-Encoding
Date: Thu, 15 Feb 2018 18:49:48 GMT
Connection: keep-alive
Transfer-Encoding: chunked

{"group":{"_id":"yJHQRaDFrakdggzAM","name":"private9","fname":"private9","t":"p","msgs":33,"u":{"_id":"3WpJQkDHhrWPBvXuW","username":"admin"},"customFields":{"company":"sell-and-more"},"ts":"2018-01-21T21:04:41.008Z","ro":false,"sysMes":true,"_updatedAt":"2018-02-15T18:49:48.877Z","topic":{"a":"b"}},"success":true,"developerWarning":"[WARNING]: The \"usernames\" field has been removed for performance reasons. Please use the \"*.members\" endpoint to get a list of members/users in a room."}

[geekgonecrazy]

First off thanks for the contribution! :)

Could you add a test? An example can be found: https://github.com/RocketChat/Rocket.Chat/pull/9519/files#diff-406bb36e7f1ca7e4d64c498ccb326fb8

Also a docs PR? A good example: https://github.com/RocketChat/docs/pull/527
You actually have most of that here in the PR body :)

We're trying to make sure going forward we keep api endpoints from breaking, as well as make sure developers can find it.

[xbolshe]

@geekgonecrazy I added tests (see above) and docs.

[engelgabriel]

Documentation: https://github.com/RocketChat/docs/pull/600