Add command to publish the GBM release

[jhnstn]

This command should:

• Find the release PR on Gutenberg-Mobile
• Checkout the release branch and update GB to the release tag (if needed, see comments)
• Use the gh api to create a new release

[jhnstn]

In most cases I suspect we won't have to update GB since the new release prepare gb command handles all the commits.
But we might need to add a change to the GB PR so this command should check to see if GB is current and if not update the ref and run the bundle command.

[jhnstn]

Question: Should we make sure the GBM release pr has been approved before creating the release ?