Connectors: Register Akismet Anti-Spam as a default connector

[jorgefilipecosta]

Summary

Register Akismet Anti-Spam as a built-in non-AI connector with spam_filtering type.

• Uses the existing wordpress_api_key WordPress option for API key storage
• Checks the WPCOM_API_KEY PHP constant

Testing

Verify the akismet connector works as expected:

• Test the default activation flow.
• Delete Akismet and test the installation flow. Set an Akismet key verify it shows as connected, on the connectors and on the Akismet own settings page.
• Set a key on Akismet settings page verify it is reflected on the connectors screen.
• Set a key using wp-config define( 'WPCOM_API_KEY', 'your-key' ); verify the connectors reflect the key was set on wp-config.

See also: WordPress/gutenberg#76828

[github-actions]

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[jorgefilipecosta]

Only this part is relevant the rest is Gutenberg ref update which is included for testing but will not be part of the commit.

[github-actions]

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