[crd-gen] Support openAPIV3Schema fields: minimum, maximum, pattern, nullable

Is your enhancement related to a problem? Please describe

(duplicate of #2959)

At the moment there is no way to auto generate a crd (with crd-gen tool) that contains properties with validation fields like minimum, maximum, pattern, nullable.

CRD example:

...

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: tenants.example.com
spec:
  group: example.com
  names:
    kind: Tenant
    plural: tenants
    singular: tenant
  scope: Namespaced
  versions:
  - name: v1
    schema:
      openAPIV3Schema:
        properties:
          spec:
            properties:
              kafka:
                type: object
                properties:
                  port:
                    type: integer
                    minimum: 0
                    maximum: 65535
                    nullable: false
                  hostname:
                    type: string
                    pattern: '^([A-Za-z0-9-]{1,63}\.)+[[A-Za-z0-9-]{1,63}$'
                    nullable: false
                nullable: false
...

Describe the solution you’d like

I’d like to use javax annotation (like @min @max @pattern) on a java model fields.

private String protocol;

@Pattern(regexp = "\\^\\(\\[A-Za-z0-9-]\\{1,63}\\\\\\.\\)\\+\\[\\[A-Za-z0-9-]\\{1,63}\\$")
private String hostname;

@Min(0)
@Max(65535)
private Integer port;

Currently @NotNull annotation generate the filed “required” on crd, but for “nullable” validation maybe we need of a new specific annotation.

Describe alternatives you’ve considered

No response

Additional context

version: 5.12.2

[andreaTP]

Closed in #4348

[andreaTP]

I’m about to go on vacation, but if no one picks it up earlier I might eventually take a look at this.