[GX-17505] Dismantle core-plugin

[DanielSanudo]

Summary

Changelog

Test Plan

[Swaagie]

Did you want to mention middleware functions here?

[Swaagie]

are these spies reset and cleaned, probably want to use sinon as sandbox here

[DanielSanudo]

This comes from const { spy, stub } = require('sinon');.
I am not creating global mocks or anything, do they need to be reset and clean?

[Swaagie]

Good improvement in itself, but most of our warehouse modules use a license badge rather than adding section at the bottom. I think we want to be consistent, but not feeling strong about it at this point

[kinetifex]

I think this should be changed up slightly in a couple of ways:

1. Let's not pass devServer through these several lifecycles. gasket.command === 'local' will always be available and it looks like only the nextjs-plugin needs it for nextApp.
2. Let's make the createServers lifecycle an execWaterfall, which gives plugins the opportunity to adjust the createServers options (serverOpts). In our initial case, the express-plugin will add the handler to the config object, rather than just return a handle for the https-plugin to add. This will allow more flexibility and should be easier to document.

[kinetifex]

Yea, probably should await this, in case there are modifications that affect things down the chain.

Also, probably would be most clear for consuming hooks to name these instances as next, and express:
exec('nextExpress', { next: app, express: expressApp })

[kinetifex]

For some high-level context for additional reviewers, below is lifecycle flow @DanielSanudo and I discussed which he implemented here, to dismantle the core-plugin, where x means hook and -> means execute lifecycle.

build (command)
    x nextjs-plugin

start (command)
    x https-plugin
        -> createServers
        x express-plugin
            -> middleware
            -> express
                x nextjs-plugin
                    -> initWebpack()
                        x webpack-plugin
                            -> webpack
                            -> webpackChain
                    -> nextConfig
                    -> next
                    -> nextExpress (was ssr)
            -> errorMiddleware
        -> servers

[kinetifex]

@DanielSanudo also, you'll need these generator files moved to the nextjs-plugin:
https://github.com/godaddy/gasket/tree/core-plugin/packages/gasket-core-plugin/generator

All except .gitignore.template and .gitignore.template, which I'm proposing will be owned by a git-plugin: #26

[kinetifex]

Update serverOpts with http/https also before passing to lifecycle