* Adds a changelog page, linked from the main, with content
automatically loaded from the source. To avoid conflicts, each entry
is its own file and entries are grouped by the month during which
the update will (probably) be deployed
* The last group (most likely "last update") doesn't have a title, the
rest do.
* Add changelog entries from the last update so it's not too empty.
* Also update the layout for the alerts a bit: remove bottom margin to
reduce loss of whitespace.
* 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.
