Feature/add multisite support from cli

[dsawardekar]

Description of the Change

This PR adds support for Multisite WordPress installations via the WP CLI commands.

• The find command now supports a --network option
• The index command also supports a --network option
• The delete-index command also supports a --network option

The --network option will iterate over all the sites on a Multisite install. It also accepts a comma delimited list of site_ids to limit the operation to subset of sites, eg:- --network=1,2.

You can also combine the --network option with the --count option to get a summary of a block's usage across the network.

How to test the Change

• Pull this branch locally
• Network activate the block-catalog plugin on a Multisite install
• Run the index with wp block-catalog index --network
• Search for blocks across the network

Changelog Entry

Added - Multisite Support via WP CLI with the --network option

Credits

Props @dsawardekar

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.

[Sidsector9]

Tests well on both single and multisite installs 👍