Add slack footers to link directly to workflow logs

[WVerlaek]

Description

Adds a slack footer for all Slack messages posted from a workflow, with a direct link to the workflow logs:

The existing Actions URL in the message only links you to the page showing all GHA runs for that commit, and there you'd have to find the workflow run you need. With the footer you can directly go to the workflow run.

This change has been used already for a while in the workspace e2e tests here, see Slack message for example

Related Issue(s)

How to test

Documentation

Preview status

gitpod:summary

Build Options

Build

• /werft with-werft
  Run the build with werft instead of GHA
• leeway-no-cache
• /werft no-test
  Run Leeway with --dont-test

Publish

• /werft publish-to-npm
• /werft publish-to-jb-marketplace

Installer

• analytics=segment
• with-dedicated-emulation
• workspace-feature-flags
  Add desired feature flags to the end of the line above, space separated

Preview Environment

• /werft with-local-preview
  If enabled this will build install/preview
• /werft with-preview
• /werft with-large-vm
• /werft with-gce-vm
  If enabled this will create the environment on GCE infra
• with-integration-tests=all
  Valid options are all, workspace, webapp, ide, jetbrains, vscode, ssh
• with-monitoring

/hold

[WVerlaek]

/unhold