[Authorization] Extend privileges config to support OR evaluations

[elena-shostak]

Currently, our requiredPrivileges structure supports allRequired and anyRequired for defining authorization logic. However, there is a need to support more complex scenarios as (privilege1 AND privilege2) OR (privilege3 AND privilege4)

To achieve this we can extend anyRequired, which will allow for defining multiple AND conditions evaluated with OR logic:

security: {
  authz: {
    requiredPrivileges: [
      { anyRequired: [['privilege1', 'privilege2'], ['privilege3', 'privilege4']] }
    ]
  }
}

An array of arrays aka privilege groups where each inner group represents a set of privileges that must all be present (AND logic). The outer array represents OR logic between these groups.
So it will evaluate to: (privilege1 AND privilege2) OR (privilege3 AND privilege4)

The following needs to be done:

• Modify the security config interface to extend anyRequired definition.
• Implement logic to evaluate new anyRequired conditions.
• Update existing documentation to include the new structure.
• Write tests to validate the logic.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)