Docs/beta: update the RPC changelog

This MR updates the RPC changelog for beta.

The new documentation can be found here: https://tezos.gitlab.io/-/tezos/-/jobs/7383883101/artifacts/docs/_build/protocols/beta.html#rpc-changes

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR