Allow to define random seed when generating scalar examples

[nitrotm]

The code used to generate the sample values uses Math.random which cannot be initialized with a seed:

spectaql/src/themes/default/helpers/graphql-scalars.js

Line 2 in 9f38a4e

import { mocks } from 'graphql-scalars'

cf. https://github.com/Urigo/graphql-scalars/blob/master/src/mocks.ts

Would it be possible to copy this logic here to replace Math.random with something else, like:

https://github.com/michaeldzjap/rand-seed

and add a config option to initialize the seed to a fixed value and reset this on every query example maybe? That would be very helpful to generate static examples every time spectaql is executed.