Update gitignore file to allow checkout as a wp-content directory.

[peterwilsoncc]

Bug Description

For developing on environments other than wp-env, the performance repo needs to be checked out as the wp-content directory.

It would be great to update the repo's gitignore file to allow for this by:

• ignoring all files and folders in the plugins directory
• ignoring all files and folders in the themes directory
• allow listing the plugins that live in this mono-repo

This will prevent a dirty git environment when installing other plugins.

Steps to reproduce

1. Checkout this repo to run as wp-content
2. Install WP
3. Install Query Monitor
4. Observe a dirty repo

Screenshots

Additional Context

I use Chassis for my development environment for WordPress, Gutenberg and other WP plugins. This allows me to run the code on a different system config that most people are using for developing WP projects... it's very effective at picking up bugs.

[westonruter]

I personally do have the performance repo checked out in wp-content/plugins, and then I have symlinks just that point into the performance/plugins subdirectory:

auto-sizes@ -> performance/plugins/auto-sizes
dominant-color-images@ -> performance/plugins/dominant-color-images
embed-optimizer@ -> performance/plugins/embed-optimizer
image-prioritizer@ -> performance/plugins/image-prioritizer
optimization-detective@ -> performance/plugins/optimization-detective
performance-lab@ -> performance/plugins/performance-lab
speculation-rules@ -> performance/plugins/speculation-rules
view-transitions@ -> performance/plugins/view-transitions
web-worker-offloading@ -> performance/plugins/web-worker-offloading
webp-uploads@ -> performance/plugins/webp-uploads

[westonruter]

This should get documented in the handbook: https://make.wordpress.org/performance/handbook/performance-lab/