[legacy-framework] add ability to increase bodyParser size for queries & mutations

[flybayer]

Closes: blitz-js/legacy-framework#114

What are the changes and their implications?

Add ability to increase bodyParser size for queries & mutations, same as for API routes.

You can export a config object from a blitz query or mutation like this:

export const config = {
  api: {
    bodyParser: {
      sizeLimit: "2mb",
    },
  },
};

Feature Checklist

• Integration test added (see test docs if needed)
• Documentation added/updated (submit PR to blitzjs.com repo)