Adding Cloud Pod release and test workflows

[steffyP]

This PR adds workflows to automatically create Cloud Pod releases, and to test the released Cloud Pods on a weekly basis.

Releasing Cloud Pods

• cloudpod_release.yml can be run manually
  • set the release-tag for the release-version
  • be aware, that the release-tag is the same tag as the LocalStack version tag, that is used to create pod.
• it will re-create a release for latest for any pushes on main (e.g. we assume that the code changed).
• A release will automatically be created or updated, including pods for mariadb and mysql
• The release notes contain a Cloud Pod Launchpad as well.
• In theory, we can create a release for any LocalStack version by running the workflow, and setting the release-tag (which will be used for both: the LocalStack version and the version of the release)

Testing Cloud Pods

• test_cloudpods.yml is scheduled to run weekly
• it contains a slack notifications hook, which will notify our dedicated slack channel if anything fails
  • NOTE: I decided not include the diagnose file, as I think it will be too big.
  • If the tests fail, we have the chance identify any regression with cloud pods
  • new version of the cloud pod must be created manually then
• the workflows checks every released version, and injects the pods (for each flavor), and runs the smoke tests
• also added the gautamkrishnar/keepalive-workflow which will add empty commits to make sure the workflows stay active.

Known Issue

• the cloudpod tests are not stable yet (sometimes the lambda cannot connect to the database for both engines)
• we will tackle this issue later on, as it seems very specific to this sample
• we could disable the cloudpod test workflow in the meantime
• I tested the cloudpod (for mysql) on my local machine, it worked as expected.

README

• updated the README to contain information about Cloud Pods and the Launchpad