### Summary

Using docker_container_exec's stdin syntax doesn't decrypt vaulted variables.

I was suggested in https://github.com/ansible-collections/community.docker/issues/241 that it's most likely issue with Ansible, not the collection.

### Issue Type

Bug Report

### Component Name

docker_container_exec

### Ansible Version

```console
$ ansible --version
ansible [core 2.11.6]
  python version = 3.9.7 (default, Sep 10 2021, 14:59:43) [GCC 11.2.0]
  jinja version = 3.0.3
  libyaml = True
```


### Configuration

```console
$ ansible-config dump --only-changed
ANSIBLE_NOCOWS(/home/user/.ansible.cfg) = True
CACHE_PLUGIN(/home/user/.ansible.cfg) = jsonfile
CACHE_PLUGIN_CONNECTION(/home/user/.ansible.cfg) = /tmp/ansible-cachedir
CACHE_PLUGIN_TIMEOUT(/home/user/.ansible.cfg) = 5
DEFAULT_GATHERING(/home/user/.ansible.cfg) = smart
DEPRECATION_WARNINGS(/home/user/.ansible.cfg) = False
DIFF_ALWAYS(/home/user/.ansible.cfg) = True
HOST_KEY_CHECKING(/home/user/.ansible.cfg) = False
```


### OS / Environment

- Target: Ubuntu 20.04.3

### Steps to Reproduce

```yaml
    - name: Upload key
      community.docker.docker_container_exec:
        argv:
          - tee
          - secret.json
        container: '{{ docker_id }}'
        stdin: '{{ secret_data | to_json }}'
```

Var file (vaulted value is embedded):

```
secret_data:
  priv_key:
    value: !vault |
        $ANSIBLE_VAULT;1.1;AES256
        1161...
        ....
  pub_key:
    value: some_public_key
```

### Expected Results

Vaulted variable is properly decrypted.

I've tested encryption with:

```
ansible localhost -m ansible.builtin.debug -a var=secret_data -e @all/vars.yml
```

and the syntax is valid (variable is decrypted as expected), but not when using docker collection.

### Actual Results

```console
JSON file which was created consist ansible vault data, not decrypted string.

 below
"value": {"__ansible_vault": "$ANSIBLE_VAULT;1.1;AES256;\n1161...
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
''' takes a list of dicts with each having a 'key' and 'value' keys, and transforms the list into a dictionary,
        effectively as the reverse of dict2items '''
    if not is_sequence(mylist):
        raise AnsibleFilterTypeError("items2dict requires a list, got %s instead." % type(mylist))
    return dict((item[key_name], item[value_name]) for item in mylist)
def path_join(paths):
    ''' takes a sequence or a string, and return a concatenation
        of the different members '''
    if isinstance(paths, string_types):
        return os.path.join(paths)
    elif is_sequence(paths):
        return os.path.join(*paths)
    else:
        raise AnsibleFilterTypeError("|path_join expects string or sequence, got %s instead." % type(paths))
class FilterModule(object):
    ''' Ansible core jinja2 filters '''
    def filters(self):
        return {
            
            'b64decode': b64decode,
            'b64encode': b64encode,
            
            'to_uuid': to_uuid,
            
            'to_json': to_json,
            'to_nice_json': to_nice_json,
            'from_json': json.loads,
            
            'to_yaml': to_yaml,