Add notice about webhooks using the legacy REST API

[Konamiman]

Changes proposed in this Pull Request:

This pull request is an extension of #40535. It:

1. Adds a new WebhookUtil::get_legacy_webhooks_count method. It counts the existing webhooks that are configured to use the Legacy REST API classes to generate their payloads.
2. Adds a new api_version optional argument to WC_Webhook_Data_Store::search_webhooks.
3. Adds a new "Legacy" section to the webhooks settings page, it lists the same webhooks that are counted by get_legacy_webhooks_count.
4. Adds a new warning notice that is shown if at least one of these legacy webhooks exist and the separate Legacy REST API extension doesn't exist:

Note that if legacy webhooks exist and the Legacy REST API is enabled, two notices will appear. This is on purpose, it's better to be "overinformative" in this case and the notices can be dismissed anyway.

How to test the changes in this Pull Request:

1. If you tested Add notices about the removal of the Legacy API in WooCommerce 9.0 #40535 and have the dummy Legacy REST API plugin installed, disable it.
2. Make sure that no webhooks exist that are configured with "Legacy API v3" in the "API Version" field (WooCommerce - Settings - Advanced - Webhooks, you need to edit a webhook to see the API version it's using).
3. Run the following to simulate a WooCommerce update from the point of view of the admin notices: wp eval 'WC_Admin_Notices::reset_admin_notices();'
4. Verify that no new notices appear when reloading any admin page.
5. Create a couple of new webhooks (or edit existing ones) so that they have "Legacy API v3" in the "API Version" field.
6. Repeat step 3.
7. Reload the webhooks list page. Note how the "The WooCommerce webhooks with Legacy REST API payload will be unsupported soon" notice has appeared and that there's a new "Legacy" section.
8. Go to the new "Legacy" section, verify that it lists the appropriate webhooks.
9. Delete the webhooks, or edit them to use a different API version.
10. Reload any admin page, the notice should have disappeared.
11. Repeat step 5, then step 3, the notice should appear again upon reload.
12. Create a dummy Legacy REST API plugin (see the testing instructions of Add notices about the removal of the Legacy API in WooCommerce 9.0 #40535, step 11) unless you have done that already. Activate the plugin.
13. Repeat step 3, reload, the notice should have disappeared.
14. Try also manually dismissing the notice (to revert that: wp db query "delete from wp_usermeta where meta_key='dismissed_legacy_webhooks_unsupported_in_woo_90'").

Changelog entry

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Significance

• Patch
• Minor
• Major

Type

• Fix - Fixes an existing bug
• Add - Adds functionality
• Update - Update existing functionality
• Dev - Development related task
• Tweak - A minor adjustment to the codebase
• Performance - Address performance issues
• Enhancement - Improvement to existing functionality

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[github-actions]

Hi @coreymckrill,

Apart from reviewing the code changes, please make sure to review the testing instructions as well.

You can follow this guide to find out what good testing instructions should look like:
https://github.com/woocommerce/woocommerce/wiki/Writing-high-quality-testing-instructions

[github-actions]

Test Results Summary

Commit SHA: 7949d74

Test 🧪	Passed ✅	Failed 🚨	Broken 🚧	Skipped ⏭️	Unknown ❔	Total 📊	Duration ⏱️
API Tests	259	0	0	2	0	261	0m 57s
E2E Tests	215	0	0	4	0	219	20m 7s

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To view the full API test report, click here.
To view the full E2E test report, click here.
To view all test reports, visit the WooCommerce Test Reports Dashboard.

[coreymckrill]

Works as described in the excellent testing instructions. A couple of wording suggestions, and one small concern about caching.

[coreymckrill]

👍 Confirmed that the legacy count is accurate with Docket Cache enabled. Everything else looks good as well.

[coreymckrill]

@Konamiman I'm not sure why some of the checks are failing, you might want to do a rebase if this was branched before #40572 got merged...