Cannot change connector plugin type while adding/editing a Search API Server

Problem/Motivation

When adding or editing a Search API Server, after selecting Backend = ElasticSearch, changing the ElasticSearch Connector radio button has no effect: it always shows the configuration form for Configure Standard ElasticSearch Connector.

In the console, the error An error occurred during the execution of the Ajax response: TypeError: $wrapper[method] is not a function is displayed when you select a different connector plugin.

Steps to reproduce

1. Follow the steps in Set up a local 8.0.x environment.
2. Log in
3. Go to /admin/modules, check Key, then click the Install button.
4. Go to /admin/config/search/search-api/add-server
5. Set Backend = ElasticSearch. In the Configure ElasticSearch backend details element, you see a ElasticSearch Connector set of radio buttons. The Standard option is selected by default. Below is a details element with the title Configure Standard ElasticSearch connector.
6. Set ElasticSearch Connector = Elastic Cloud ID.
   • Expected behavior: the details element with the title Configure Standard ElasticSearch connector is replaced with a details element with the title Configure Elastic Cloud ID ElasticSearch connector
   • Actual behavior: the details element with the title Configure Standard ElasticSearch connector does not change

Proposed resolution

Turns out this is a result of Use replaceWith, not replace, in #ajax form settings which was introduced in 10.3.0 in #3303557: Deprecate and remove the AJAX replace method.

Update src/Plugin/search_api/backend/ElasticSearchBackend.php; change the $form['connector']['#ajax']['method'] from 'replace' to 'replaceWith'.

Remaining tasks

1. Create a merge request — merge request !170 for 9.0.x created by @mparker17 in #2
2. Create a merge request — merge request !171 for 8.0.x created by @mparker17 in #4
3. Community review/feedback — skipped by @mparker17 in #7
4. Maintainer review/feedback — done by @mparker17 in #7
5. Commit to 9.0.x — done by @mparker17 in #8
6. Commit to 8.0.x — done by @mparker17 in #10
7. Release 9.0.x — released in 9.0.0-alpha2
8. Release 8.0.x — released in 8.0.0-alpha6

User interface changes

None.

API changes

None.

Data model changes

None.