[installer-tests] Add slack webhook for test failures

[nandajavarma]

Description

This PR adds slack webhook alerting capabilities to the nightly tests. Currently if any of the setup fails, alert goes to #self-hosted-jobs channel on slack and if any of the integration tests fails it goes to the corresponding team's job channel (currently only workspace and IDE).

Related Issue(s)

Fixes #11273

How to test

You can run any tests like in this internal doc to check the alerts

Release Notes

NONE

Documentation

Werft options:

• [ ] /werft with-preview

[nandajavarma]

/hold waiting to confirm with teams before sending out alerts

[nandajavarma]

/unhold

[andrew-farries]

/hold as this is blocking the merge pool.

It looks like it needs rebased onto main, to pick up the gofmt changes: https://github.com/gitpod-io/gitpod/pull/11958

[nandajavarma]

Sorry about that, @andrew-farries ! Rebased and builds are passing. unholding! /unhold

[andrew-farries]

/unhold