Support hashicorp vault?

[bitsofinfo]

Describe the solution you'd like
Support vault as a backend for secrets.

What is the added value?
Having new backends increases chances for adoption and broadens the operator use cases.

Give us examples of the outcome

apiVersion: store.externalsecret-operator.container-solutions.com/v1alpha1
kind: SecretStore
metadata:
  name: secretstore-sample
spec:
  controller: staging
  # Sample store types
  #
  # Vault  
  store:
    type: vault
    auth: 
      secretRef: 
        name: externalsecret-operator-credentials-vault
        namespace: externalsecret-operator-system
    parameters:
      server: vault.example.com
      path: /vault/path

Observations (Constraints, Context, etc):

[riccardomc]

Hi there! Thank for your interest in our project!

Vault is definitely on our radar and we have people that expressed their interest in having a backend for it already.

Our plan is to reach the 0.1.0 milestone before adding more backends. We are quite close: https://github.com/ContainerSolutions/externalsecret-operator/milestone/1 Part of this milestone is documenting how to add new backends which will make contributing much easier.

This said, any contribution is already more than welcome 😄

[knelasevero]

Related to #89