Adds ability to manage plugins for self hosted sites that aren't connected to Jetpack

[emilylaguna]

Fixes #16595
WordPressKit Related PR: wordpress-mobile/WordPressKit-iOS#406

This adds self hosted non-Jetpack users the ability to manage the plugins on their site.

Demo

plugin-demo.mov

To test:

WordPress Site that is not Jetpack Connected

1. Switch to the site in the My Site view
2. Swipe down to find that the Plugin section is visible
3. Verify you can view your sites plugins
4. Verify you can make a plugin active
5. Verify you can deactivate a plugin
6. Verify you can install a plugin
7. Verify you can uninstall a plugin

WordPress Site that is connected to Jetpack

1. Switch to the site in the My Site view
2. Swipe down to find that the Plugin section is visible
3. Verify you can view your sites plugins
4. Verify you can make a plugin active
5. Verify you can deactivate a plugin
6. Verify you can install a plugin
7. Verify you can uninstall a plugin

WordPress Hosted Atomic Site

1. Switch to the site in the My Site view
2. Swipe down to find that the Plugin section is visible
3. Verify you can view your sites plugins
4. Verify you can make a plugin active
5. Verify you can deactivate a plugin
6. Verify you can install a plugin
7. Verify you can uninstall a plugin

WordPress Hosted Simple Site

1. Switch to the site in the My Site view
2. Swipe down to find that the Plugin section is NOT visible

WordPress Site that is running WordPress 5.4 or below

1. Switch to the site in the My Site view
2. Swipe down to find that the Plugin section is NOT visible

Regression Notes

1. Potential unintended areas of impact

• This affects the logic for showing the Plugin management section

2. What I did to test those areas of impact (or what existing automated tests I relied on)

• Manual testing with each type of site (simple, atomic, self hosted, self hosted running below WordPress 5.5)
• added unit tests for the plugin management logic

3. What automated tests I added (or what prevented me from doing so)
   Unit Tests / UI Tests

• New units tests I added

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger an installable build for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[yaelirub]

@emilylaguna , I get a crash when I run on your branch, it has conflicts and irrelevant commits. Can you please fix?

[emilylaguna]

@emilylaguna , I get a crash when I run on your branch, it has conflicts and irrelevant commits. Can you please fix?

Interesting! Looks like the Zendesk pod got updated and is causing issue. Fixing it now.

[emilylaguna]

@leandroalonso I found an issue when installing a plugin the view state would reset and just say 'Install'. I fixed this in this commit: 3c163b8 which pairs the plugin obj with a directory object if it's missing/nil.

[leandroalonso]

Tested all the scenarios, all good!

[leandroalonso]

Can you please add (Don't apply to Jetpack app) before the change description?

[emilylaguna]

Done! 426ad9c