Support for subcommand aliases

[thibgc]

It would be great to be able to take advantage of argparse's ability to give subcommands one or more aliases. Example of help output in plain argparse:

    delete-files (df)   cause the files to be deleted
    reload-files (rf)   cause the files to be reloaded
    validate-files (vf)
                        cause the files to be validated

Equivalent in plain argparse:

        subparser = parser.add_parser('delete-files',
                                      aliases=['df'],
                                      description='Subcommand for deleting files',
                                      help='cause the files to be deleted')

and similar. Of course currently there are any number of workarounds -- in my projects I'm working on, I do things like:

class MyModel(BaseModel):
    delete_files: Optional[DeleteFilesModel] = Field(description='cause the files to be deleted', alias='delete-files')
    df: Optional[DeleteFilesModel] = Field(description='synonym for: delete-files')

etc. but it results in longer help output:

    delete-files        cause the files to be deleted
    df                  synonym for: delete-files
    reload-files        cause the files to be reloaded
    rf                  synonym for: reload-files
    validate-files      cause the files to be validated
    vf                  synonym for: validate-files

Note that there's a difference in need between alias='delete-files' and aliases=['df'] so having both alias and aliases might be very confusing; perhaps aliases needs to be something like subcommand_aliases.

Thanks for considering!