Improve CORS env. variables

[jsenko]

There are some CORS variables missing, and ALLOWED_ORIGINS should also include Keycloak URL.
Example:

- name: CORS_ALLOWED_ORIGINS
  value: >-
    http://keycloak-apicurio-registry-e2e.apps.rkubis13.apicurio.integration-qe.com,
    http://registry-apicurio-registry-e2e.apps.rkubis13.apicurio.integration-qe.com
- name: CORS_ALLOWED_METHODS
  value: 'GET,PUT,POST,PATCH,DELETE,OPTIONS'
- name: CORS_ALLOWED_HEADERS
  value: >-
    x-registry-name,x-registry-name-encoded,x-registry-description,x-registry-description-encoded,x-registry-version,x-registry-artifactid,x-registry-artifacttype,x-registry-hash-algorithm,x-registry-content-hash,access-control-request-method,access-control-allow-credentials,access-control-allow-origin,access-control-allow-headers,authorization,content-type