add utilities so we can send Slack notifications if proxy errors happen

[I-Dont-Remember]

What was changed?

• Adding necessary utilities to allow us to get a Slack client and send a message to the user who created an event config if a webhook proxy fails.

Why is this good for our users?

This is good because without it, these background errors would never be surfaced anywhere. This is a first step, there is probably a better way to surface more information if we find that people are heavily using the proxy capabilities.

Attestation

Below you'll find a checklist. For each item on the list, check one option and delete the other.

• Unit Tests
  • [x] Unit tests have been updated.
• Documentation
  • [x] This change does not need a documentation update.
• Integration Testing
  • [x] At minimum, ran the ./test_workflows/workflow_buddy_end_to_end_test_read_only.slackworkflow workflow and it was both successfully completed & outputs looked correct (We don't have a way to assert that changes are correct yet).