Improve the process of creating font packages

[siddhantk232]

fastn has a guide on how to create a Font Package (https://fastn.com/create-font-package/). This guide is not easy to follow because it:

• Asks users to install python
• Asks you to clone one repository and then create a totally different repository and copy-paste files between these two

Ideally a fastn subcommand should take care of:

• Talking to google fonts (maybe other font hosts as well)
• Reading available configurations and translate them to fastn.font
• Creating a default set of ftd.type-data
• Providing both a) create a separate font package that is publishable b) add output to current fastn package

[amitu]

Should be part of fastn xtask crate?