OpenApi3 - For responses, use Reason Phrase as description instead of status code

Is: Responses description is the string value of the status code. Example:

responses:
"400":
description: "400"

Should: Response description should have the description defined by [section 10 of RFC 2616](https://datatracker.ietf.org/doc/html/rfc2616#section-10). Example:

responses:
"400":
description: "Bad Request"

If not mistaken the line of code is this one:
https://github.com/ePages-de/restdocs-api-spec/blob/b4bd4bb89787af215b49a13264fa122df8f547b8/restdocs-api-spec-openapi3-generator/src/main/kotlin/com/epages/restdocs/apispec/openapi3/OpenApi3Generator.kt#L337

Perhaps also the option to customize this description.