External vault storage

[jahvon]

Enhancement Summary

There are many tools out there that are already great at secret management. It would be nice to have a pattern for integrating external secret / password management systems into flow so that secrets don't need to be copied out of those system on to local machines.

Additional context

Lots to consider here, including:

• How does flow authenticate to those systems in a standard way
• How can the available integrations be expanded upon in a light-weight way
• What systems should be integrated to start
• How does a flow secret reference map to external secret references/IDs

This should all be configurable, of course.