Add hooks functionality

[sergiordlr]

Add support for hooks functionality

In order to add a hook to a migration plan, add this variable to the migration (or in the defaults/main.yml file of the test role)

- name: Execute migration
  include_role:
    name: migration_run
  vars:
    migration_hooks:
    - hook_name: automaticpreback
      custom: false
      target_cluster: source
      playbook: "{{ lookup('template', 'hook.yml.j2') | string }}"
      execution_namespace: robot-source
      service_account: robot-source
      phase: PreBackup

Allowed target_custers
target_cluster: destination
target_cluster: source

Allowed phases
phase: PreBackup
phase: PostBackup
phase: PreRestore
phase: PostRestore