### 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
else:
            
            module.fail_json(msg="{0} must be installed and visible from {1}.".format(apt_pkg_name, sys.executable))
    if not repo:
        module.fail_json(msg='Please set argument \'repo\' to a non-empty value')
    if isinstance(distro, aptsources_distro.Distribution):
        sourceslist = UbuntuSourcesList(module)
    else:
        module.fail_json(msg='Module apt_repository is not supported on target.')
    sourceslist_before = copy.deepcopy(sourceslist)
    sources_before = sourceslist.dump()
    try:
        if state == 'present':
            sourceslist.add_source(repo)
        elif state == 'absent':
            sourceslist.remove_source(repo)
    except InvalidSource as ex:
        module.fail_json(msg='Invalid repository string: %s' % to_native(ex))
    sources_after = sourceslist.dump()
    changed = sources_before != sources_after
    if changed and module._diff:
        diff = []
        for filename in set(sources_before.keys()).union(sources_after.keys()):
            diff.append({'before': sources_before.get(filename, ''),
                         'after': sources_after.get(filename, ''),
                         'before_header': (filename, '/dev/null')[filename not in sources_before],
                         'after_header': (filename, '/dev/null')[filename not in sources_after]})
    else:
        diff = {}