[FEATURE]: rename `policy` field in policy configuration flow

[araujof]

Summary

Improve naming and configuration surface for CPEX authz configuration.

Details

Currently, we have two fields in an authz configuration flow in CPEX: policy and post_policy. We also have identity to signify authentication requirements, and define authorization flows as sequences of args, policy, post_policy, results groups:

global: # for global authz flows, applied to any targets
  identity: [...]
  args: [...]
  policy: [...]
  ...

routes:  # for per-entity authz flows
  - tool: get_employee
    authentication:
      - jwt-user
      - jwt-client
    args:
      employee_id: "str"
    policy:
      - "require(authenticated)"
      - "delegation.depth > 2: deny"
    result:
      ssn: "str | redact(!perm.view_ssn)"
      salary: "int | redact(!role.hr)"
      employee_id: "str | mask(4)"
    post_policy:
      - run(...)

We would like to improve naming and organization of this configuration. A proposal:

global:
  authentication:
    - jwt-user
    - jwt-client
  authorization:
    pre_invocation: [...]
    post_invocation: [...]

routes:
  - tool: get_compensation
    identity: [...]
    args:
      employee_id: "str"      
    authorization:
      pre_invocation:
        - "require(authenticated)"
        - "delegation.depth > 2: deny"
      post_invocation:
        - "run(...)"        
    result: 
        ssn: "str | redact(!perm.view_ssn)"
        salary: "int | redact(!role.hr)"
        employee_id: "str | mask(4)"

Note: args and result are not recognized under global group.

Acceptance Criteria

• Unit tests
• Regression testing with Praxis