feat: runbook snapshot create

[benPearce1]

This is WIP, not complete

Notes to future me: This is currently only supporting creating a new snapshot and publishing it - which is a bit wrong. Publishing an existing snapshot requires POST to the runbook with an update to the PublishedRunbookSnapshotId property set to the snapshot id

This should be changed to be two commands: runbook snapshot create with an optional --publish parameter runbook snapshot publish to publish an existing snapshot: runbook snapshot publish --runbook "runbook name" --snapshot "Snapshot QWE123"

will probably fix https://github.com/OctopusDeploy/cli/issues/110