Feature request - Rule to detect deprecated commands or features

I'd like to see an existence-style rule with a list of deprecated or otherwise banned commands and even features. The main intent is to detect them being used in code blocks and warn about the usage of a deprecated feature.

For example, `juju run-action`.

Review the repository's existing existence-style rules and how they inspect code blocks. Determine where a list of deprecated commands or features would be defined and how warnings are expressed, using `juju run-action` as the example; done means the rule reliably warns when listed items appear in code blocks.

Written by the indexing model from the issue text.