Problem:

If we ever leak license signing keys, we want to be able to generate new ones. But, we can't start using a new key until after the public key has been added to a released version of Coder. So, we can't just take the latest key, we need to be configured.

AC:

1. export LICENSOR_KEY_BUCKET to a Google Cloud Bucket containing multiple keys
2. export LICENSOR_KEY_ID to the older key in the bucket
3. start the server
4. generate a license
5. verify the license uses the correct key
6. stop the server and change LICENSOR_KEY_ID to another key in the bucket
7. start the server
8. generate a license
9. verify the license uses the correct key

Note: automated unit testing is generally not required for this repo