Blueprints: Link created stacks to source

Stacks created by Blueprints should have an explicit link to their creating blueprint that’s easy to find. For example, blueprint-created stacks should automatically get a label like `source:

blueprint/ajtest-011-01JX9T6S13755Z5CNTQCVGJQ20`. The presence of this label can be used in the Web UI to link a stack back to the creating Blueprint.