Feat/graphiql plugins #892

[codeflyer]

Allow injection of graphiql plugins in the configuration of a mercurius server:

app.register(mercurius, {
  schema,
  resolvers,
  graphiql: {
    enabled: true,
    plugins: [
      {
        name: 'samplePlugin',
        props: {},
        umdUrl: 'http://localhost:3000/graphiql/sample.js',
        fetcherWrapper: 'parseFetchResponse'
      }
    ]
  }
})

Closes #892

[ilteoood]

LGTM

[mcollina]

lgtm

[simoneb]

LGTM

[simoneb]

nit: this isn't JS code (use sh for formatting properly) and you can omit "./"

[simoneb]

this method on the reply comes from fastify/static, doesn't it? I wouldn't make the assumption that people know. either use a different method or make it more explicit where it's coming from

[mcollina]

@simoneb can this land? I'd like to ship a release soon.

[simoneb]

good to go 👌