Add support for command and subcommand aliases

[gilles-stragier]

Feature Request: Add support for command and subcommand aliases

As discussed in #132 (comment), there's a need for official alias support in Typer.

Examples needed:

• Command aliases: list → ls, remove → rm
• Subcommand aliases: versions → ver → v, documents → docs

Current workaround:

@app.command("list")
@app.command("ls", hidden=True)  # Hidden alias

Requested feature:

Official alias support that doesn't clutter help output and provides a clean API for creating command shortcuts.

This would bring Typer in line with other popular CLI tools that support aliases natively.