Bump secrets plugin protocol version to 2

[carolynvs]

What does this change

Version 1 is the old protocol that only supported Resolve.
Version 2 is the new protocol with gRPC, context.Context and the new Create function.

What issue does it fix

Part of #1027

Notes for the reviewer

We should reference the constant defined in Porter from the plugins so that when the plugin references porter to get the protocol interface they automatically get the correct version of the protocol.

getporter/azure-plugins#41
getporter/kubernetes-plugins#108

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR