Add Expected Command Arguments

Commands are triggered based on the `CommandWord` only. We should have expected arguments for commands. This would also mean that `!so` and `!so DevChatter` could be handled differently, since the former needs to do a random selection based on an API call and the latter does a simple text replacement.

Start by locating the command dispatch that currently matches CommandWord, then trace the !so handling and its API call or text-replacement path. Define how expected arguments distinguish !so from !so DevChatter, and verify that both command forms produce their intended behavior.

Written by the indexing model from the issue text.