Including beta/RC offers in the updates endpoint

[danielbachhuber]

Would it be worth the effort to include beta/RC offers in the updates endpoint?

Context:

It would be great if WP-CLI supported a version flag such as wp core update --version=beta which stuck to the current beta/RC in the same way that the beta tester plugins appears to.

From ​https://github.com/wp-cli/core-command/issues/17

cc @johnbillion

[dd32]

This is something that has come up in the context of core and "update channels" - being able to select to be on a bleeding edge (trunk), advance preview (beta/RC), preview (RC), or stable (current release).

We'd likely not support just the "beta releases" (Beta1, 2 ... ), but rather a flag which once specified, starts delivering the development nightlies once the nightlies is past alpha and into beta, etc.

The beta tester simply specifies $wp_version + 0.2 to the update api to receive the current trunk nightlies, regardless of alpha/beta/rc status, which is not too helpful in some scenario's.
(edit: This was covered in the linked github thread, and turns out we do have some extra magic handling for the beta-tester plugin, to keep it within branch even after branching)

[dd32]

This has been implemented on WordPress.org, You should be able to use #5412 and/or ​#core51319