Expose "check and set" write option and secret version to read (K/V 2)

[trailrunner-taulia]

• Expose the the "check and set" option for optimistic locking behavior on secret write operation
• Expose the secret version from the metadata block on secret read operation response so it can be used for "check and set"

Corresponding API documentation https://www.vaultproject.io/api/secret/kv/kv-v2.html

[settermjd]

This looks like what I'm after to be able to retrieve a secret's version. Is there any chance of it being merged?