BE: RBAC: Impl default role

[seono]

I’ve opened a draft PR. If this approach looks okay, I’ll follow up with tests and documentation.

• Breaking change? (if so, please describe the impact and migration path for existing application instances)

What changes did you make? (Give an overview)
Implement default role
#344

Is there anything you'd like reviewers to focus on?
I updated each extractor’s extract method to return the defaultRole if it’s present, but I’m not sure if this aligns with the original intention of how extract is supposed to be used.

I tested it using the configuration below

rbac:
  default-role:
    name: defaultRole
    permissions:
        - resource: clusterconfig
          actions: [ view ]

        - resource: topic
          value: ".*"
          actions: 
            - VIEW
            - MESSAGES_READ

        - resource: consumer
          value: ".*"
          actions: [ view ]

        - resource: schema
          value: ".*"
          actions: [ view ]

        - resource: connect
          value: ".*"
          actions: [ view ]

        - resource: acl
          actions: [ view ]
  roles: []

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• No need to
• Manually (please, describe, if necessary)
• Unit checks
• Integration checks
• Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

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