gh-35891: Deprecate sorting by default in connected component methods for graphs
Fixes #35889.
### :books: Description
We deprecate sorting by default in `connected_components` and
`connected_component_containing_vertex`. The default value of parameter
`sort` was `True`. We change it to `None` to identify calls when a
deprecation warning is necessary. We also add parameter `key` so that
users can define home made sorting rules.
This deprecation is needed to avoid type errors when vertices have
labels of incomparable type.
### :memo: Checklist
<!-- Put an `x` in all the boxes that apply. It should be `[x]` not `[x
]`. -->
- [x] The title is concise, informative, and self-explanatory.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
- [x] I have updated the documentation accordingly.
### :hourglass: Dependencies
URL: https://github.com/sagemath/sage/pull/35891
Reported by: David Coudert
Reviewer(s): Dima Pasechnik
