Community template support for init command

[aklinker1]

I've consistently said no to adding content to the templates:

• Update the content of content.ts to the corresponding template content. #552
• When creating a template, it is recommended to include a "Hello world" example with 1 test case. #325
• Add some features to the CLI #369
• Extend CLI functionality #187

Templates are a huge time sink to keep up to date and the more features/variants that are added, the more time it takes away from me to add features and fixes to WXT itself.

That said, I'm open to adding community template support to the init command!

Originally posted by @aklinker1 in #570 (comment)