docker: Use mpm_event and php-fpm instead of mpm_prefork and mod_php

[anomiex]

Proposed changes:

The main hope here is that using mpm_event rather than mpm_prefork will make our E2E tests run better.

But mod_php is not compatible with mpm_event. The modern way to do things is to use php-fpm instead.

And while we're at it, we may as well enable apache's http2 module too. Although actually making effective use of that may take more work (if anyone cares), since HTTP/2 likes to run with TLS but our dev environment doesn't do TLS.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

pc9hqz-2f3-p2#comment-1825

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Temporarily change

  jetpack/tools/docker/docker-compose.yml

  Line 37 in 9e6f6dc

  image: automattic/jetpack-wordpress-dev:latest

  to refer to ghcr.io/automattic/jetpack-wordpress-dev:pr-33783 and restart your docker env (jetpack docker stop && jetpack docker up -d). Then make sure everything still works.
• If you can run the E2E tests locally and reproduce the kinds of problems mentioned in pc9hqz-2f3-p2, see if this helps.

[github-actions]

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[zinigor]

Works well for me!