add multiple auth; AND/OR schemes

some disabled tests are here: https://github.com/Kong/openapi2kong/blob/c78767704bd66c81477829bf95510b7a634db636/spec/testfiles/security.yaml#L45-L62

Not everything can be supported:

* multiple key-auth in an AND fashion is not supported by Kong
* multiple key-auth in OR fashion can be added in a single plugin config
* one securityRequirements object (with entries in AND) can be supported (except for muyltiple key-auth as mentioned above)
* multiple securityRequirements objects can be supported only if they all have max 1 entry, since that would resolve in a generic OR (multiple key-auth can be done in OR as mentioned above)

To figure out:
* how can be combine Oauth2 and OIDC in and/or fashion. Does that even make sense??
* http only supports 'basic', what if it supports others? according to OpenAPI docs the ['bearerFormat' property is only a hint](https://swagger.io/specification/#securitySchemeObject), so is it even possible?

Start with the disabled cases in spec/testfiles/security.yaml, lines 45–62. Compare those cases with the listed Kong limitations and unresolved OAuth2, OIDC, and HTTP questions; done means the supported AND/OR combinations are decided and the relevant tests can be enabled or updated.

Written by the indexing model from the issue text.