# What this PR does
Semi-related to https://github.com/grafana/oncall-private/issues/2131
Addresses occasional task failures for
`apps.slack.tasks.update_slack_user_group_for_schedules` when trying to
update a Slack user group for a non-paid Slack account. [Slack's
documentation](https://slack.com/help/articles/212906697-Create-a-user-group)
mentions this is a paid only feature, hence the error
([logs](https://ops.grafana-ops.net/goto/-AWfsrrIR?orgId=1) from an
actual task):
```
2024-08-08 16:20:36,613 source=engine:celery worker=ForkPoolWorker-16 task_id=6bdaae94-1552-4b6d-93e2-e2fa0bae57b1 task_name=apps.slack.tasks.update_slack_user_group_for_schedules name=apps.slack.models.slack_usergroup level=WARNING Slack usergroup S06LW5GJ88Z update failed: Slack API error! Response: {'ok': False, 'error': 'paid_teams_only'}
```
Updated our docs on our Slack integration to emphasize that this feature
_only_ works for paid Slack accounts
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
`release:`). These labels dictate how your PR will
show up in the autogenerated release notes.
Do not retry updating a message if Slack returns `cant_update_message`
API [error](https://api.slack.com/methods/chat.update#errors) (meaning
bot user has no permission to update the message).
# What this PR does
- Rename `SlackClientWithErrorHandling` to just `SlackClient`
- Add more error classes + improve the way errors are raised based on
the Slack error code
- Add API call retries on Slack server errors (e.g. when Slack returns
`5xx` errors)
- Refactor some methods working with Slack API + add tests
## Which issue(s) this PR fixes
- https://github.com/grafana/oncall-private/issues/1837
- https://github.com/grafana/oncall-private/issues/1840
- https://github.com/grafana/oncall-private/issues/1842
## Checklist
- [x] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)
