Add release-automation pipelines

[christian-kreuzberger-dtx]

Right now creating a release is manual work.

Take a look at https://github.com/keptn-contrib/dynatrace-service and https://github.com/keptn/go-utils to get some release automation using Github actions.

However, please keep in mind, that releasing an Azure DevOps extension is a little bit more complicated.

• Add AZDO_PUBTOKEN to secrets in this repo
• Set proper version based on tag coming from pre-release/release workflow
• Create & Upload vsix file to visual studio market place
• Ensure GitHub release is in sync with Visual Studio Market Place.

Please use the commands from

• https://github.com/keptn-sandbox/keptn-azure-devops-extension/blob/master/README_DEV.md#create-public-release-vsix-package
• https://github.com/keptn-sandbox/keptn-azure-devops-extension/blob/master/README_DEV.md#publish-private-or-public-release

Known Limitation: The extension will be published in VS Marketplace, but the GH release will stay as draft
this will be addressed with keptn/gh-automation#13

Definition of Done

• A new pre-release can be created via triggering a pipeline (private; as "Cloud Automation Integration [DEV]")
• A new release can be created via triggering a pipeline (published; as "Cloud Automation Integration")
• Each release results in a VS Marketplace entry and a GH release
• Release notes are automatically generated
• Versions are automatically updated/set
• Link to Marketplace entry is in GitHub Release