Hidden commands are still shown within our documentation

Summary

doc/source/using_commands.rst uses Click's API in order to auto-generate some documentation for our commands.

Since the landing of our artifact and source subcommands, we've had to 'hide' some of the pre-existent commands, for example bst track -> bst source track, where the former is hidden like so: https://gitlab.com/BuildStream/buildstream/blob/master/buildstream/_frontend/cli.py#L1123

Unfortunately, the hidden commands are still present in our documentation of the top level command bst: https://docs.buildstream.build/using_commands.html#bst

What is the expected correct behaviour?

• The hidden commands should not be present in the documentation

Possible fixes

Unless I've missed something, this looks to me like an upstream, sphinx-click, bug.

• An upstream issue has been filed: https://github.com/click-contrib/sphinx-click/issues/33
• An upstream PR has also been created: https://github.com/click-contrib/sphinx-click/pull/34/files

Update

The first upstream issue was closed via https://github.com/click-contrib/sphinx-click/pull/32, however this has not fixed our issue, hidden commands are still being shown as valid options when we generate the documentation for bst.

As a stop gap, !1097 (merged) has landed, this ensures that "COMMAND OBSOLETE" is present in both the man pages and the documentation of our hidden commands.