Automatically create PR for a new stargate release

[ivansenic]

Once a new version is released on stargate/stargate we should create a new PR for this repository automatically. In order to do this:

• ~create script that replaces the version in all necessary files~ done in #59
• create webhook that can be trigger from the stargate/stargate (pass new version as the payload)
• create workflow that creates a new PR based on the new version of Stargate and is fired on the webhook call
• extend Stargate release workflow to ping the webhook using peter-evans/repository-dispatch

[tatu-at-datastax]

Done for Stargate V2 so I think this can be closed.