Provides a less manual interface for creating the freeze:
* takes the name of the branch to create
* takes any number of PRs which must be part of the freeze
* takes PRs representing the HEADs of the new branches
Then essentially takes care of the test.
Implementation of the actual wizard is not trivial but fairly
straightforward and linear, biggest issue is not being able to
`project_id.branch_ids[1]` to get the new branch, not sure why but it
seems to ignore the ordering, clearing the cache doens't fix it.
When creating the branches, add a sleep after each one for secondary
rate limiting purposes. Same when deleting branches.
Also the forwardbot has been updated to disable the forwardport cron
while a freeze is ongoing, this simplifies the freezing process.
Note: after recommendation of @aab-odoo, tried using `_applyChanges`
in `_checkState` but it simply did not work: the two relational fields
got completely frozen and were impossible to update, which is less
than ideal. Oh well, hopefully it works well enough like this for now.
* Cherrypicking is handrolled because there seems to be no easy way to
programmatically edit commit messages during the cherrypicking
sequence: `-n` basically squashes all commits and `-e` invokes a
subprocess. `-e` with `VISUAL=false` kinda sorta works (in that it
interrupts the process before each commit), however there doesn't
seem to be clean status codes so it's difficult to know if the
cherrypick failed or if it's just waiting for a commit of this step.
Instead, cherrypick commits individually then edit / rewrite their
commit messages:
* add a reference to the original commit
* convert signed-off-by to something else as the original commit was
signed off but not necessarily this one
* Can't assign users when creating PRs: only repository collaborators
or people who commented on the issue / PR (which we're in the
process of creating) can be assigned.
PR authors are as likely to be collaborators as not, and we can have
non-collaborator reviewers. So pinging via a regular comment seems
less fraught as a way to notify users.
