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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
```
new_vault_ids = []
            if encrypt_vault_id:
                new_vault_ids = default_vault_ids
            if context.CLIARGS['new_vault_id']:
                new_vault_ids.append(context.CLIARGS['new_vault_id'])
            new_vault_password_files = []
            if context.CLIARGS['new_vault_password_file']:
                new_vault_password_files.append(context.CLIARGS['new_vault_password_file'])
            new_vault_secrets = \
                self.setup_vault_secrets(loader,
                                         vault_ids=new_vault_ids,
                                         vault_password_files=new_vault_password_files,
                                         ask_vault_pass=context.CLIARGS['ask_vault_pass'],
                                         create_new_password=True)
            if not new_vault_secrets:
                raise AnsibleOptionsError("A new vault password is required to use Ansible's Vault rekey")
            
            
            new_encrypt_secret = match_encrypt_secret(new_vault_secrets,
                                                      encrypt_vault_id=encrypt_vault_id)
            self.new_encrypt_vault_id = new_encrypt_secret[0]
            self.new_encrypt_secret = new_encrypt_secret[1]
        loader.set_vault_secrets(vault_secrets)
        
        vault = VaultLib(vault_secrets)
        self.editor = VaultEditor(vault)
        context.CLIARGS['func']()
        
        os.umask(old_umask)
    def execute_encrypt(self):