Adds new changes to main #1175 Branch: OpenApiRepository and Validation

[tschlat]

Implement new features:

• a repository for OpenApis
• validation based on atlassian OpenAPI validator framework

Note that with respect to validation, there are now two different validators. One which is based on standard citrus validation mechanism and one based on atlassian framework. The later is much more powerfull but might raise more issues. We should make a decision on how to proceed here:

• Remove standard citrus implementation and rely on atlassian validation
• Use both as is. Since atlassian validation is performed message level, it comes first and citrus most probably is never called.
• Have cirtus kick in, when atlassian is disabled (possible by configuration and on a per request basis)

[bbortt]

We should make a decision on how to proceed here:

I am personally ok with "hardening" features when it comes to feature releases - which it is.

The later is much more powerfull but might raise more issues.

I don't think that has to be breaking necessarily, as long as the API itself (e.g. OpenAPI must be stored in a different directory, leading to false-positives because no spec is loaded at all) does not break.

Edit: Tho it may break a bit more, when thinking about it. We would then remove apicurio entirely, right?