[FEATURE]: Allow plugins to be installed from github directly

[eznix86]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

I think for velocity or even for testing, it would nice to be able to install plugins directly from github instead of npm.

Bun supports it.

Example

// opencode.json
{
  "plugin": [
    "github:eznix86/myfancyplugin#main"
  ]
}