Rotation: Sanity check there are enough members

[Asartea]

Because

• It doesn't make sense to swap or rotate members if there are less than two members
• Trying to do without enough members seems to cause all kinds of fun issues: Bug - points command: Symbols aren't escaped #571 (comment)

This PR

• Adds a sanity check: if there are less than two members in the queue and the actionType isn't add or remove, it immediately returns with a message

Pull Request Requirements

• I have thoroughly read and understand The Odin Project Contributing Guide
• The title of this PR follows the location of change: brief description of change format, e.g. Callbacks command: Update verbiage
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If this PR adds new features or functionality, I have added new tests
• If applicable, I have ensured all tests related to any command files included in this PR pass, and/or all snapshots are up to date

[MaoShizhong]

Will review after merging #611 because you'll likely need to resolve a small merge conflict.