CLI: Add install command

[kraftbj]

Changes proposed in this Pull Request:

• Adds jetpack install which runs composer install and yarn install if composer.json or package.json are present in a project.

Also, prettifies the build step:

Screen.Recording.2021-01-22.at.5.26.01.PM.mov

Jetpack product discussion

n/a

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

n/a

Testing instructions:

• yarn install for the initial install.
• Either run yarn cli-link or prefix all of the commands below with .tools/cli/bin/, e.g. ./tools/cli/bin/jetpack install --help.
• jetpack to see all help commands.
• jetpack install --help to see the install commands.
• jetpack install to get a project picker.
• jetpack install --root to get a project picker and install the monorepo root too.
• jetpack install monorepo to install the monorepo root without a project.
• jetpack install packages/connection to install that particular package.
• jetpack install packages/connection --root to install a particular package and the repo root.
• jetpack build plugins/jetpack to see the new build prettification.

Proposed changelog entry for your changes:

Screen.Recording.2021-01-22.at.3.19.34.PM.mov

[kraftbj]

@anomiex I want to DRY out the command a bit, but end of my day so wanted to push up to get a gut check that this makes you happy wrt the github action providing verbose output. https://github.com/Automattic/jetpack/pull/18504/checks?check_run_id=1826705537

[anomiex]

Haven't checked the code yet, but the verbose output looks fine to me.

If I were writing an action-specific tool I'd put a ::group::Installing $SLUG before the [23:35:53] Installing $SLUG [started] line and ::endgroup:: after the corresponding [23:36:06] Installing $SLUG [completed], so the GH Actions log would group and collapse each tool's install commands. Which, if you really want to do, you could look for an appropriate environment variable to trigger that. But unless it's super easy to do it I wouldn't bother since this isn't an action-specific tool, and at least there is clear grouping even if GH doesn't pick up on it.

[kraftbj]

Going to land this. If there are more issues, this is under active iteration and we'll keep with it.

[anomiex]

Suggested change

	* @param {object} tasks - The tasks object
	*
	* @returns {object} An array of either the root install task or empty.
	* @param {Array} tasks - The tasks array
	*
	* @returns {Array} The tasks array, which may have been modified.