### Summary

The `apt_repository` will fail with a somewhat confusing error if gnugp, and dirmngr manager are not installed.  Neither of these packages are Required/Essential/Important, and may not be already installed in minimal systems that you might want to run `apt_repository` on.

The fix might be to just include `gnupg` in the requirements section of the docs.

### Issue Type

Documentation Report

### Component Name

apt_repository

### Ansible Version

```console
$  ansible --version
ansible [core 2.11.4]
  config file = ...
  configured module search path = ...
  ansible python module location = ...
  ansible collection location = ...
  executable location = /usr/local/bin/ansible
  python version = 3.9.2 (default, Feb 28 2021, 17:03:44) [GCC 10.2.1 20210110]
  jinja version = 3.0.1
  libyaml = True
```


### Configuration

```console
$ ansible-config dump --only-changed
```


### OS / Environment

Mostly a docs issue so this is N/A. But apt_repository applies to Debian, Ubuntu, and forks.

### Additional Information

Tells people that need gnupg when using apt_repository.

### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
module = AnsibleModule(
        argument_spec=dict(
            repo=dict(type='str', required=True),
            state=dict(type='str', default='present', choices=['absent', 'present']),
            mode=dict(type='raw'),
            update_cache=dict(type='bool', default=True, aliases=['update-cache']),
            update_cache_retries=dict(type='int', default=5),
            update_cache_retry_max_delay=dict(type='int', default=12),
            filename=dict(type='str'),
            
            install_python_apt=dict(type='bool', default=True),
            validate_certs=dict(type='bool', default=True),
            codename=dict(type='str'),
        ),
        supports_check_mode=True,
    )
    params = module.params
    repo = module.params['repo']
    state = module.params['state']
    update_cache = module.params['update_cache']
    
    sourceslist = None
    if not HAVE_PYTHON_APT: