Summary

This PR can be summarized in the following changelog entry:

• Adds a checkbox to use the AI staging API.

Relevant technical choices:

• I've added the checkbox in the "Enable development mode" section, which I renamed "Development settings" since the sections are already a lot and sometimes too fine-grained.
• We have opted to not bust the usermeta settings about the API token for now, since after chaning the setting it would need to happen for all the users in a site. This means that the first request after switching from production to staging or vice versa will fail and then after the code generates a new token it will work again.
  This results in 1 try again needed after every switch.

Milestone

• I've attached the next release's milestone to this pull request.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Install with Premium containing this PR and check that the AI feature works with and without the checkbox ticked.
  note that there is no way to check in the plugin which URL is actually used so we are basically performing a regression test.

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Fixes #194