Don't stop on read-only mode for read-only storage workflows

Summary:
Fixes T11042. Currently, all bin/storage workflows stop if cluster.read-only is set:

$ ./bin/storage adjust
Usage Exception: Phabricator is currently in read-only mode. Use --force to override this mode.

However, some of them (status, dump, databases, etc) are read-only anyway and safe to run. Don't prompt in these cases.

Test Plan:

• Set cluster.read-only to true.
• Ran bin/storage dump, bin/storage status, etc. No longer received messages.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11042

Differential Revision: https://secure.phabricator.com/D15987