Add Hooks on Access/Refresh Token Errors

[n7studios]

Summary

Adds the WordPress hooks convertkit_api_get_access_token_error, convertkit_api_refresh_token_error and convertkit_api_access_token_invalid, which Kit Plugins may use to e.g. delete invalid access/refresh tokens from their Plugin settings.

Removes the is_production_site check, so that non-production sites may automatically refresh expired access tokens. This check was introduced in this PR in September 2024, as a workaround prior to the tenant_name support which was added in November 2024. As such, it's no longer needed, as each site is issued its own tokens.

Testing

Existing tests pass.

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
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• 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)

[noelherrick]

Makes sense, but in our own consumers, we need to check to make sure we're only deleting the tokens when the Kit service says they're invalid or expired, not if there's a rate limit or a 5xx error.