Create pipeline to automatically update Iron Bank image on every bbctl version bump

#197 (closed) introduces a helm chart that will be built and distributed as part of the Big Bang umbrella. This helm chart pulls a hardened, Iron Bank image with bbctl preinstalled. This build is configured here: https://repo1.dso.mil/dsop/big-bang/bbctl. We need to create an automated way of keeping this build up-to-date with the latest builds of bbctl as feature development is completed.

To update the Iron Bank image, an MR that updates the target image tarball needs to be made

Acceptance Criteria

• Create a pipeline that triggers on merge to main when the bbctl version number is bumped (we don't need new builds for docs changes, for instance) that opens a new MR against the Iron Bank repo that:
  • Updates all version tags and docs
  • Updates the target binary the Iron Bank build will pull here to pull the latest image

Blocked by the tarball build and release process to be implemented in #218