[Feature Request]: Add a Variable Resolver for Hashicorp Vault

[mattcasters]

What would you like to happen?

I would love to have a way to resolve variables directly against a Hashicorp Vault server.
It should allow me to enter a path and a value to look up, for example:

#{vault:dwh/some-db:hostname} should resolve to some hostname.

We should always resolve to the String representation of the value in the secret.

Issue Priority

Priority: 3

Issue Component

Component: Other

[mattcasters]

See also: issue #3454