Document SSM agent limitations

**What I'd like:**

The AWS variants include the SSM agent for accessing the console interface and retrieving node information. There are additional commands users can run via the `aws ssm` command line. Some of these commands are relevant for Bottlerocket and some are not.

`AWS-UpdateSSMAgent` is one that doesn't work since Bottlerocket does not allow packages to be updated for a running instance. There are likely more. `AWS-RunPatchBaseline` appears to be another one.

Rather than leaving it up to our users to figure out what works and what doesn't, we should provide some documentation that lets users know what to expect. This doesn't need to be an exhaustive list of SSM agent commands. That is better documented elsewhere. But we should at least point out some of the main commands or type of commands that users should be aware are not relevant when working with Bottlerocket.

No target file or test is named. Start by locating the website's existing Bottlerocket and SSM documentation, then document representative commands such as AWS-UpdateSSMAgent and AWS-RunPatchBaseline that are not relevant, along with the command categories users should treat cautiously; done means users can understand the main limitations without an exhaustive command list.

Written by the indexing model from the issue text.