Secret (version) handling improvements

[lkubb]

What does this PR do?

• Adds support for reading specific versions of KV v2 secrets
• Adds support for restoring secret versions on KV v2
• Adds support for deleting/destroying all versions of secrets on KV v2
• Adds support for destroying the latest version without knowing its number on KV v2
• Adds support for completely wiping the metadata of a secret path on KV v2
• Adds state module for statefully managing secrets

What issues does this PR fix or reference?

Fixes: #61
Fixes: #62

Previous Behavior

Mostly ignorant about KV v2 versions.

New Behavior

More specific handling of KV v2 versions possible.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes