This was a bit trickier than I anticipated, because there's no good
ways to avoid passing the credentials around manually.
What's basically happening now is that the credentials for the state
bucket are checked in (encrypted), and sourcing `creds.fish` uses the
cloud HSM to decrypt and load them into the environment.
Change-Id: I3f5ce1c9bd9d5efbf1013414f94771a09ea3a488
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8494
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
