Add ansible collection support

[tod-uma]

This PR makes it possible to use the splunk-ansible repository with ansible-galaxy as a collection. This makes it useful to integrate splunk-ansible with other ansible projects.

For example, I use this to add the splunk universal forwarder to all of our machines as a part of our bootstrap process. Here is the code I can now use:

collections/requirements.yml

collections:
  -  source: <url to repo>                
     version: ansible-collection
     type: git

and run the following command to install the collection:

ansible-galaxy collection install -vvv -r collections/requirements.yml --force

then in my playbook (splunk_universal_forwarder.yml):

- name: splunk_universal_forwarder playbook                                     
    hosts: splunk_universal_forwarder                                             
    become: true                                                                  
    collections: 
      -  splunk.splunk_ansible                                            
    vars:                                                                         
      splunk: "{{ splunk_universal_forwarder }}"  # set the splunk variable however you want, we use group_vars variables                                
    tasks:
    - name: "prepare the machine here"                                               
      ansible.builtin.debug:                                                    
        msg: "put tasks to get the machine ready here"
    - name: "install the forwarder"                                             
      ansible.builtin.include_role:                                             
        name: splunk_universal_forwarder

you can then run the playbook like:

ansible-playbook -v --limit <target host> splunk_universal_forwarder.yml

I had to move the library directory to plugins/modules so that ansible could find the plugins correctly in the collection environment. This should more universally work.

The galaxy.yml I build is very minimal, just enough to get it to work. I would expect it would need modified to better match the project.

Documentation on ansible collection development can be found at https://docs.ansible.com/ansible/latest/dev_guide/developing_collections.html

Documentation on ansible galaxy support can be found at https://docs.ansible.com/ansible/latest/dev_guide/collections_galaxy_meta.html#collections-galaxy-meta