new: Add support for Parent/Child account switching

[lgarber-akamai]

📝 Description

This change adds preemptive support for the Parent/Child Account Switching feature, including the following changes:

• New endpoint methods:
  • client.ListChildAccounts(...)
  • client.GetChildAccount(...)
  • client.CreateChildAccountToken(...)
• Updated structs:
  • linodego.User now contains a UserType field

In addition to the above changes, this change brings the linodego.Account struct up to parity with the current API response.

This change also makes the following testing/helper changes:

• The test package now has a unit directory for storing mock tests
• The test package now imports testify/require to make tests more concise

Depends on #458

✔️ How to Test

The following test steps assume you have pulled down this PR locally and are using the token and URL for a parent account in dev.

Unit Testing

make testunit

E2E Testing

make ARGS="-run TestUser" fixtures
make TEST_TAGS="parent_child" ARGS="-run TestAccount" fixtures

Manual Testing

1. In a manual testing environment (e.g. dx-devenv), run the following script:

package main

import (
	"context"
	"fmt"
	"log"
	"os"

	"github.com/linode/linodego"
	"github.com/sanity-io/litter"
)

func main() {
	ctx := context.Background()

	client := linodego.NewClient(nil)
	client.SetToken(os.Getenv("LINODE_TOKEN"))

	childAccounts, err := client.ListChildAccounts(ctx, nil)
	if err != nil {
		log.Fatal(err)
	}

	childAccount, err := client.GetChildAccount(ctx, childAccounts[0].EUUID)
	if err != nil {
		log.Fatal(err)
	}

	token, err := client.CreateChildAccountToken(ctx, childAccount.EUUID)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println("Child Accounts:")
	litter.Dump(childAccounts)

	fmt.Println("\nChild Account:")
	litter.Dump(childAccount)

	fmt.Println("\nChild Account Token:")
	litter.Dump(token)
}

2. Ensure the output looks similar to the following:

Child Accounts:
[]linodego.Account{
  linodego.Account{
    FirstName: "DX-Child",
    ...
  },
}

Child Account:
&linodego.Account{
  FirstName: "DX-Child",
  ...
}

Child Account Token:
&linodego.Token{
  ID: ...,
  Token: ...,
}

[yec-akamai]

Existing tests are passing 👍

[lgarber-akamai]

Going to convert this back to a draft while I work to break some of the smaller changes into separate PRs

[zliang-akamai]

TEST_TAGS wasn't added into the Makefile?
make TEST_TAGS="parent_child" ARGS="-run TestAccount" fixtures doesn't run any test case on my end..

[zliang-akamai]

Everything else tested and looks good!

[lgarber-akamai]

@zliang-akamai Oops, looks like it was accidentally dropped when I was fixing some merge conflicts. I can fix it real quick 👍

[zliang-akamai]

Nice work!

[yec-akamai]

Nice work! Change looks good to me.

Unit tests and user tests passed locally. I still don't have the 1pass vault set up for my account, so can't run through the parent/child integration tests on my end.