Add plugin.js support

[stevefan1999-personal]

Sometimes it would be better to use a full blown script for plugin manifest because we can use it to resolve some complicated stuff and future type stubs for code safety*. This practice is basically everywhere. SWC, ESLint, Mocha, Jest all allows such use.

For my own sake, this also added a slightly good benefit of lexicographically sorting the fields thanks to ESLint. My OCD hits when I see the fields not being sorted from A to Z.

*: if you used a TypeScript transpiler, that is what most people should start doing.

Missing

• Tests
• Examples: https://github.com/stevefan1999-personal/nodebb-plugin-stub

[julianlam]

I am not opposed to defining plugin configuration information this way :+1:

[stevefan1999-personal]

@barisusakli @psychobunny what you guys think?