✨ Add support for rich_help_panel of commands in generated docs

[kinuax]

The generated Markdown docs ignore the division given by rich_help_panel while listing the commands. This is a proposal to support it.

[kinuax]

I added the tests to verify the cases with default (None, "", "Commands") and custom panel titles. All format, linting, and tests pass locally on 3.11. CI only breaks on 3.7 with a syntax error due to the walrus operator (introduced on 3.8). Having that Python 3.7's end of life was almost a year ago and that click dropped 3.7 support 9 months ago, I wonder if this is a good moment to drop its support as well, I can take care of that before considering these changes.

[kinuax]

As clarified at #830, click still supports 3.7 so I have refactored to avoid assignment expressions and pass 3.7 tests. Tests are updated too to verify mixed commands in same app and pass coverage. Ready to be reviewed.

[svlandeg]

Tricky merge conflict with #944, which has changed the order of commands being displayed. Should be all good and green again.

[kinuax]

@svlandeg, many thanks for checking this out and fixing the merge conflicts! 🙏

[svlandeg]

I think this is a nice feature! I tested it with

typer docs_src/commands/help/tutorial006.py utils docs

to see the difference between master and this PR, and you nicely get the subdivision in the markdown with this PR:

whereas on master it's just:

There's a few issues with the code though. I'll comment inline, and will put the PR in draft as I push some changes.

[svlandeg]

I think this is ready for review by Tiangolo.

One final remark I have here is that this code is not tested in our test suite without having rich installed. This is why the initial implementation didn't result in a test failure, while it really should have. #1297 should improve that situation (that said, I think these PRs can be reviewed/merged independently).