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##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
Whenever I use `ansible-vault encrypt_string`, I want to take the result and add it to a variable file, however I have to manually select the text/copy/open file for editing/paste/save the change.  This process is painful especially when you have multiple strings to encrypt as it doesn't work with the Unix way of things thus being very manual.   I thought `ansible-vault encrypt_string --output` might be something to help here, but the help documentation is confusing as it appears this is only used with `encrypt` and `decrypt` _(commands)_.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
lib/ansible/cli/vault.py

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
The only way I can see this working _without coming up with custom file descriptors or repurposing stderr for encrypted output so redirection will work_ is to add a new option that could append the resulting string to a file.
```shell
ansible-vault encrypt_string --encrypt-vault-id default --stdin-name --append vars_file.yml
Reading plaintext input from stdin. (ctrl-d to end input)
hunter22
Encryption successful
```
stderr=True)
                display.display('The last named variable will be "%s". The rest will not have'
                                ' names.' % context.CLIARGS['encrypt_string_names'][-1],
                                stderr=True)
            
            for extra_arg in args[len(name_and_text_list):]:
                name_and_text_list.append((None, extra_arg))
        
        else:
            name_and_text_list = [(None, x) for x in args]
        
        for name_and_text in name_and_text_list:
            name, plaintext = name_and_text
            if plaintext == '':
                raise AnsibleOptionsError('The plaintext provided from the command line args was empty, not encrypting')
            b_plaintext = to_bytes(plaintext)
            b_plaintext_list.append((b_plaintext, self.FROM_ARGS, name))
        
        
        outputs = self._format_output_vault_strings(b_plaintext_list, vault_id=self.encrypt_vault_id)
        for output in outputs:
            err = output.get('err', None)
            out = output.get('out', '')
            if err:
                sys.stderr.write(err)
            print(out)
        if sys.stdout.isatty():
            display.display("Encryption successful", stderr=True)
        
    def _format_output_vault_strings(self, b_plaintext_list, vault_id=None):