optimade.prefetch() method

[Valexr]

Add optimade.prefetch() method to make custom local cache

const optimade = new Optimade({
  providersUrl: "https://providers.optimade.org/providers.json",
});

optimade.prefetch({
  pathWithFileName: './prefetch.json', 
  excludeProviders: [''],
  batch: false
})

pathWithFileName - path to file output filename.json location
excludeProviders - array for exclude providers from cache
batch - portion statusable prefetching