Turn on the WordProof integration by default

[leonidasmi]

Context

Summary

This PR can be summarized in the following changelog entry:

• Turns on the WordProof integration by default

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

For enabling WordProof by default

• In a clean setup, install Yoast SEO (or clean the options using the Test Helper)
• Go to the Integrations page and confirm that the WordProof integration is enabled by default
• Go to either your privacy policy or terms and conditions (WooCommerce) page, open the Advanced collapsible in the Yoast SEO Sidebar or Metabox and confirm that you see the Timestamp with WordProof toggle.
• Now try to install the WordProof Timestamp plugin and confirm that you get a Please disable the Yoast WordProof integration before install this plugin. Go to the Yoast settings and turn off the WordProof integration message

also:

• In another clean install, first install WordProof and then install Yoast
• Confirm that the WordProof integration is not enabled by default now (because of the existence of the WordProof plugin)

For tracking whether the user has toggled the WordProof integration before

• In a clean install, enable/disable a different integration
• Confirm from the wp_options table that the wordproof_integration_changed option is set to false
• Now, disable the WordProof integration and confirm from the wp_options table that the wordproof_integration_changed option is now set to true

For multisites:

• Confirm that the WordProof integration is still not togglable for multisites

Relevant test scenarios

• [ ] Changes should be tested with the browser console open
• [ ] Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• [ ] Changes should be tested on different editors (Block/Classic/Elementor/other)
• [ ] Changes should be tested on different browsers
• [x] Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• [x] QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

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

Other environments

• [ ] This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• [ ] I have written documentation for this change.

Quality assurance

• [x] I have tested this code to the best of my abilities
• [ ] I have added unit tests to verify the code works as intended
• [ ] If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• [x] I have written this PR in accordance with my team's definition of done.

Fixes #