Child job rules should always take precedence over parent job's only/except (and vice-versa)

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Currently, if I have the following CI config:

job-a:
  only:
    refs:
      - master
  except:
    refs:
      - merge_requests
  script: echo "foo"

job-b:
  extends: job-a
  rules:
    - if: '$CI_MERGE_REQUEST_ID'
  script: echo "bar"

I get a validation error:

jobs:job-b config key may not be used with `rules`: only, except

Note that we get the same problem if jobA is defined in a template.

While the error is preventing clashing conditions, it would be great if rules from a child job could always take precedence over only/except of its parent job so that we don't get the validation error (i.e. only/except would be dropped for the job-b job since it declare rules).

Notes:

1. That this proposal should work the same if job-a is defined in a template.

2. The same thing should apply to rules (i.e. rules would be dropped for the job-b job since it declare only/except):

   job-a:
     rules:
       - if: '$CI_MERGE_REQUEST_ID'
     script: echo "foo"
   
   jobb:
     extends: job-a
     only:
       refs:
         - master
     except:
       refs:
         - merge_requests
   script: echo "bar"

This proposal would greatly ease the update of our ~"devops::secure" templates from only/except to rules (&2300 (closed)) and allow to not make this update a breaking change.