Add support for the apply_to parameter for policies

Policies were always applied to target `all` aspects and
there was no way to have them target only e.g. exchanges.
This can be important though, see [1].

This change enables the use of the apply_to parmeter via the existing
variables while maintaining `all` to be the default.

[1] https://www.rabbitmq.com/docs/parameters#how-policies-work

Change-Id: I61d68c630599b8ef2382663e8a37fdc456435c11

releasenotes/notes/applyToPolicies-f4cb13dac7ec82b0.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    RabbitMQ policies now support the `apply_to` parameter to e.g have a policy
+    target only classic_queues, exchanges, ...

tasks/rabbitmq_post_install.yml

@@ -80,6 +80,7 @@
     node: "rabbit@{{ ansible_facts['hostname'] }}"
     name: "{{ item.name }}"
     pattern: "{{ item.pattern }}"
+    apply_to: "{{ item.apply_to | default(omit) }}"
     priority: "{{ item.priority | default(0) }}"
     state: "{{ item.state | default(omit) }}"
     tags: "{{ item.tags }}"