Add a dev key to c.stage.rh.c for collection signing

Problem Description: c.stage.rh.c now supports collection signing, and the key there is the same one used in production. QE does not have the ability or desire to sign collection artifacts with the prod key, and automated tests running against c.stage.rh.c are blocked by this.

Proposed Solution:

• Add multiple keys on c.stage.rh.c - the dev key can be added alongside the prod key to the keyfile stored in vault just for stage
• Modify the entrypoint script that adds the key from the keyfile to the keystore to allow importing multiple keys