feat: add Konnect readiness validation

[johnharris85]

This PR adds a --konnect-compatibility flag to deck gateway validate that tries to codify the rules / guidelines around plugins and general configuration to make it easier for users to assess their Konnect readiness from an existing decK state (and potentially integrate into an automated pipeline).

It will check:

• If there are any plugins present that are incompatible with Konnect (e.g. oauth2)
• If there are options for specific plugins that are incompatible with Konnect (e.g. cluster strategy for RLA, etc...)
• If a _workspace is set
• If the version is incompatible (e.g. "1.1", etc...)

[mheap]

@johnharris85 LGTM - let's add some tests and ship