Do not expire HRMP open channel requests (#3543)

* Do not expire HRMP open channel requests

* Fix the build and update the docs

* Implement canceling requests and do not remove them automatically

* Fix a borked merge

* Fix fmt

* Please spellchecker

* Apply suggestions from code review

Co-authored-by: Amar Singh <[email protected]>

* Use `mutate_exists` for maintaining request counts

* Apply `rustfmt`

* Move newly introduced entrypoint to end to preserve ordering

Co-authored-by: Amar Singh <[email protected]>