Update the networking disabled error messages in wp-admin for plugins and themes

[ironnysh]

What is this PR doing?

Displays a revised error message when trying to install a new plugin or theme while networking is disabled (the default state). See #927.

What problem is it solving?

The current version of the error message doesn't include an explanation on how to enable networking.

How is the problem addressed?

Suggests two possible ways to solve the problem, including examples and links to the documentation.

Testing Instructions

Launch a Playground instance, navigate to Add Themes or Add Plugins, and see the error message.

[adamziel]

Thank you @ironnysh! I left a small request but this looks pretty good otherwise. To make the CI checks pass you'll also need to adjust the check in this E2E test:

wordpress-playground/packages/playground/website/cypress/e2e/app.cy.ts

Lines 60 to 65 in 4669959

	it('should disable networking when requested', () => {
	cy.visit('/?url=/wp-admin/plugin-install.php');
	cy.wordPressDocument()
	.find('.notice.error')
	.should('contain', 'Enable networking support in Playground');
	});

[ironnysh]

Hi @adamziel, thanks for your help! Let me know if anything is missing :-)

Thank you @ironnysh! I left a small request but this looks pretty good otherwise. To make the CI checks pass you'll also need to adjust the check in this E2E test:

[ironnysh]

Hi @adamziel, here's hoping this time it's okay :-)

Also found a hacky solution for this:

Hmm, the button is part of core. Is there a way to hide it?

and this:

The error message appears twice on the Featured plugins tab.

[adamziel]

This looks great, thank you @ironnysh! I think it's good to merge. I'll give it one more look tomorrow and then merge.

[ironnysh]

Yay! Thanks for your patience and support 🤓