notifier: adding basic oncall notifications

[alyssawilk]

Since slack google calendar support is deprecated, adding it back in via the PR notifier.
(theoretically) notifying general and oncall of rotation switches. This won't work (but will post that it doesn't work) if we do overrides incorrectly.

[repokitteh-read-only]

As a reminder, PRs marked as draft will not be automatically assigned reviewers,
or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

🐱

Caused by: #29820 was opened by alyssawilk.

see: more, trace.

[alyssawilk]

@phlax per usual sorry for my python
code is ready for review but PR is not ready to submit - I haven't updated the requirements and I'm not sure how to test that I've added them correctly. can you clue me in?

[alyssawilk]

ah, progress, found the in file, trying to figure out why I can't run pip-compile to fix the txt

[phlax]

pip-compile to fix the txt

$ pip install pip-tools
$ cd $DIR_CONTAINING_REQS
$ pip-compile --generate-hashes --reuse-hashes --allow-unsafe requirements.in

[repokitteh-read-only]

CC @envoyproxy/dependency-shepherds: Your approval is needed for changes made to (bazel/.*repos.*\.bzl)|(bazel/dependency_imports\.bzl)|(api/bazel/.*\.bzl)|(.*/requirements\.txt)|(.*\.patch).
envoyproxy/dependency-shepherds assignee is @phlax

🐱

Caused by: #29820 was synchronize by alyssawilk.

see: more, trace.

[alyssawilk]

yeah for some reason installing pip-compile didn't work. possibly python versioning, possibly google internal weirdness
python -m piptools compile --generate-hashes worked well enough with some minor differences I think I've cleaned up

[alyssawilk]

Eventual plan follow-up: associating opsgenie names with slack names so we can ping ocall from both envoy-maintainers and envoy-CI the week of rotation, and also pinging next-oncall the week before to give them a heads up rotaton will switch to them

[phlax]

assuming

NOT YET READY TO SUBMIT

is out of date

lgtm, thanks @alyssawilk