### 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
if line.startswith('ppa:'):
            source = self._expand_ppa(line)[0]
        else:
            source = self._parse(line, raise_if_invalid_or_disabled=True)[2]
        self._remove_valid_source(source)
    @property
    def repos_urls(self):
        _repositories = []
        for parsed_repos in self.files.values():
            for parsed_repo in parsed_repos:
                valid = parsed_repo[1]
                enabled = parsed_repo[2]
                source_line = parsed_repo[3]
                if not valid or not enabled:
                    continue
                if source_line.startswith('ppa:'):
                    source, ppa_owner, ppa_name = self._expand_ppa(source_line)
                    _repositories.append(source)
                else:
                    _repositories.append(source_line)
        return _repositories
def revert_sources_list(sources_before, sources_after, sourceslist_before):
    '''Revert the sourcelist files to their previous state.'''
    
    for filename in set(sources_after.keys()).difference(sources_before.keys()):
        if os.path.exists(filename):
            os.remove(filename)
    
    sourceslist_before.save()
def main():