### 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
pass
class SourcesList(object):
    def __init__(self, module):
        self.module = module
        self.files = {}  
        
        self.new_repos = set()
        self.default_file = self._apt_cfg_file('Dir::Etc::sourcelist')
        
        if os.path.isfile(self.default_file):
            self.load(self.default_file)
        
        for file in glob.iglob('%s/*.list' % self._apt_cfg_dir('Dir::Etc::sourceparts')):
            self.load(file)
    def __iter__(self):