[Feat]Support knowing the credential type used for auth for logging purposes and to upstream API.

[jeremyjpj0916]

Was glancing at this PR: #5516 and it got me thinking of another easy win feature to implement that may yield some decent return.

One thing downstream + logs do not collect was the auth pattern that was leveraged on a specific proxy transaction.

I propose an X-Authentication-Type header for upstream that all auth plugins set. Values would include:

oauth2
jwt
ldap
basic-auth
hmac

and so forth.

This idea spawns from potential analytics that can be gathered on what your most popular authentication traffic is during logging and any analysis that might be gleamed on which authentication types have the most latency or error rates etc. for further debugging.

Maybe set + get with the pdk and used in the standard Kong logs as well in basic serializer? The value can be derived from the plugins name from the conf honestly.

{
"auth": "oauth2"

or

"auth_type": "oauth2"

}

Thoughts?