Add support for a cluster setup of vaults

[BenchmarkingBuffalo]

Is your feature request related to a problem? Please describe.
I am facing the challenge to integrate with a cluster of vaults for HA reasons.
Currently this is not suported natively so I need to create my own VaultEndpointProvider, which selects a vault from the cluster and performs a healthcheck on it before returning it for further usage.

Describe the solution you'd like
I would like to have a configuration possibility to add multiple vaults like is done in spring-amqp.

Describe alternatives you've considered
It is possible to get this solution by implementing the interface VaultEndpointProvider manually.
But this approach needs to be repeated by everyone and I would like to add this functionality to the general public.
Also the usage of a load balancer in front of the vaults is not recommended: https://developer.hashicorp.com/vault/docs/concepts/ha

Additional context
If you are in general open to this approach, I can create a PR for this containing the needed changes.