v4 API: Accounts

[n7studios]

Summary

Adds support for endpoints in the accounts section of the v4 API.

Testing

• testGetAccountColors: Test that get_account_colors() returns the expected data.
• testUpdateAccountColors: Test that update_account_colors() updates the account's colors.
• testGetCreatorProfile: Test that get_creator_profile() returns the expected data.
• testGetEmailStats: Test that get_email_stats() returns the expected data.
• testGetGrowthStats: Test that get_growth_stats() returns the expected data.
• testGetGrowthStatsWithStartDate: Test that get_growth_stats() returns the expected data when a start date is specified.
• testGetGrowthStatsWithEndDate: Test that get_growth_stats() returns the expected data when an end date is specified.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• The code passes when running PHPStan
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)