Reaper: Start without S3 access key

[LtChae]

What?

Allow Reaper to start up with access to Vault but no S3 credentials

• Reaper does not crash on startup if it cannot retrieve S3 credentials from vault
• Reaper is still able to retrieve dataset secrets from Vault

Technical Notes:

• Reaper will already bypass getting S3 credentials if it does not have a secrets endpoint, but this disables dataset secret retrieval as well

Why?

Starting a new pipeline from scratch does not require Reaper to immediately have all its capabilities. Hosted datasets are rare in the current instance, and might not be needed for new instances. Adding S3 credentials to Vault is a manual process that can be avoided.

[jessicapfoster]

This is less important now because s3 access keys are a part of the process.