OpenAPI search filter HTTP 422 - add example

[rduyme]

• OpenAPI search filter HTTP 422 - add example
• Create resolvable common html page with a section for API error codes. in https://skg-if.github.io/api/ . It could be used by all implementers. It is required for type (+ title and detail content )

https://datatracker.ietf.org/doc/html/rfc7807