Fix Add Tag Functionality

[n7studios]

Summary

Fixes this reported issue, due to the maybe_tag_subscriber method checking for an API Key and Secret, instead of an Access and Refresh Token.

There are no other calls to has_api_key_and_secret, and this PR sets the has_api_key_and_secret method to deprecated, with it calling has_access_and_refresh_token and logging/displaying (depending on WordPress configuration) a notice for developers who might still be relying on this method:

In the future, it's best to remove the has_api_key_and_secret method entirely, now it's no longer used.

Testing

Tests failed to pick this up, as all tests would pre-populate the Plugin settings data in the database with an API Key and Secret, therefore ensuring that the has_api_key_and_secret condition passes.

Removed pre-populating the Plugin settings data in the database with an API Key and Secret.

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)