Description of problem:

Customer is unable to set/get Global configurations via cephadm-ansible module ceph_config. It is failing complaining that it is unable to get the current value of the global configuration value, hence it is failing. 

~~~
fatal: [rhcs5-admin]: FAILED! => changed=false 
  ansible_facts:
    discovered_interpreter_python: /usr/libexec/platform-python
  msg: Can't get current value. who=global option=osd_pool_default_size
  rc: 1
~~~

Version-Release number of selected component (if applicable):
RHCS : 16.2.10-160.el8cp
Cephadm-ansible: 1.14.0-1.el8cp
cephadm: 16.2.10-160.el8cp

How reproducible:

- It is happening all the time in both customer environment and in my test lab


Steps to Reproduce:
1. Install cephadm and cephadm-ansible
2. Write a playbook with the task using ceph_config module
3. Use global on the `who`section to set/get any global configuration value (e.g. osd_pool_default_size)
4. Run the playbook to set/get the value
5. It will fail complaining below message 
~~~
msg: Can't get current value. who=global option=osd_pool_default_size
~~~
6. If I change it from global to any other type e.g. osd or mon, the playbook is running successfully

Actual results:
The ansible playbook is failing to set/get any global configuration value

Expected results:
The playbook should be able to set/get the value

Additional info:

If I run `ceph config set global <option> <value>`, it is successfully setting the value, where as playbook is failing for the same. 

~~~
[root@rhcs5-admin cephadm-ansible]# ceph config set global osd_pool_default_size 2
[root@rhcs5-admin cephadm-ansible]# ceph config dump |grep osd_pool_default_size
global                advanced  osd_pool_default_size                  2                                                                                                                   
[root@rhcs5-admin cephadm-ansible]# 
~~~

I have an observation, although the set value is showing in `ceph config dump`, I am unable to get the same via `ceph config get global <option>` command. It is failing throwing the error `Error EINVAL: unrecognized entity 'global'`. It is working fine for other types like mon, osd etc. So I am assuming as the config get command is not working for global configs, the playbook is unable to fetch the current value and failing to set it. 

~~~
[root@rhcs5-admin cephadm-ansible]# ceph config get global osd_pool_default_size
Error EINVAL: unrecognized entity 'global'
[root@rhcs5-admin cephadm-ansible]# ceph config get osd osd_pool_default_size
2
[root@rhcs5-admin cephadm-ansible]# 
~~~

Also, I have couple of observations from the /usr/share/cephadm-ansible/library/ceph_config.py file

If I see the description of `who` I can see it is pointing to daemons. So if it is true, then I guess we can't set global config values. We need to use `mon`, `mgr`, `osd`, `client` etc, not `global`.

~~~
    who:
        description:
            - which daemon the configuration should be set to
        required: true
~~~

Then we need to modify the example section in the file where it gives example of fetching a global config value. Also, in get operation, I believe `value` should not be there. This might be a typo. 

~~~
- name: get osd_pool_default_size value
  ceph_config:
    action: get
    who: global
    option: osd_pool_default_size
    value: 1    <== Might be a typo
~~~

In this case also, customer may still want to set global values via cephadm-ansible playbook. 

If the ceph_config module is supposed to set/get global config values, then we need this to be fixed as it is failing. 

Please note, I have tested the same on RHCS 6 and it is failing there also.