Add config for `regolith config <language>_command`

[Nusiq]

Add config that let user specify where to look for the executable for a filter type.

• python.command - Python (default python)
• python.install_command - Python (default pip)
• deno.command - Deno (default deno)
• dotnet.command - .NET (default dotnet)
• java.command - Java (default java)
• nim.command - Nim (default nim)
• nim.install_command - Nim (default nimble)
• node.command - Node JS (default node)
• node.install_command - Node JS (default npm)