Shell Completion Help Text

### Describe the feature

Update the shell completer code / database to include help text in completions sent back to the Shell.

### Use Case

Whenever performing shell completion of services/attributes I want to get a short description of what the flag does.

### Proposed Solution

See #10103

This implements the changes, and exposes a Friendly Interactive SHell (Fish) implementation.

Note this implementation uses the first line of help text from command/argument help pages, so may return unexpected help text if there are problems with service docs (s3api help pages have a whole lot of `This operation is not supposed for directory buckets` - this should be fixed separately)

### Other Information

_No response_

### Acknowledgements

- [x] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CLI version used

aws-cli/2.33.28 Python/3.13.3 Linux/6.6.114.1-microsoft-standard-WSL2 source/x86_64.ubuntu.24

### Environment details (OS name and version, etc.)

WSL Linux / Ubuntu 24.04