P3-111 Adds wp-api-fetch to the classic-editor asset loading configuration

[jcomack]

Context

• Adds wp-api-fetch to the classic-editor asset loading configuration.

Summary

This PR can be summarized in the following changelog entry:

• Adds wp-api-fetch to the classic-editor asset loading configuration.

Relevant technical choices:

Test instructions

This PR can be tested by following these steps:

• Checkout this branch and build it.
• Ensure you have the Classic Editor plugin installed and activated.
• Ensure you have a valid SEMrush token.
• Create a new post (or edit an existing one).
• Add a keyphrase and hit the 'Get related keyphrases' button. A request should automatically be sent and succeed.
• Alter the database from the dropdown and click 'Change Country'
• A new request should be successfully sent.
• Check the console and ensure there are no errors.

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

[P3-111]

[JesserH]

CR&A ✅