Add a listener to track wp_mail events

[arunshenoy99]

Proposed changes

Type of Change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• Linting and tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

1. Adds a new listener to track wp_mail events.
2. Tracks whenever an email is sent successfully using the wp_mail_succeeded hook.

[ajayadav09]

Looks Good!