preload section js chunk on link hover

[namniak]

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] Feature (non-breaking change which adds functionality)
• [ ] Code style update
• [ ] Refactor (refactoring or adding test which isn't a fix or add a feature)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

Did you test your solution?

• [ ] I lightly tested it in one browser
• [x] I deeply tested it in several browsers
• [ ] I wrote tests around it (unit tests, integration tests, E2E tests)

Problem Description

Missing html resource hints ISSUE https://github.com/Jam3/nyg-jam3/issues/234

Solution Description

Created PrefetchLink component that is able to download resource on link hover. Note that in case of page links it will download a js chunk based on route string matching it with routes/keys.

Side Effects, Risks, Impact

• [x] N/A

Aditional comments: IMPORTANT

1. some browsers don't support prefetch (e.g Safari) see https://caniuse.com/#feat=link-rel-prefetch
2. there's no check for resource type whether it's downloadable or not. checking against extension would be hard to implement considering variety of supported resources. see https://caniuse.com/#feat=link-rel-prefetch
3. links with download attribute will ignore prefetch
4. there is a piece of code that needs to be maintained manually - we need to name pages chunks appropriately and match with route keys. See example:

pages/Pages.js

const Landing = lazy(() => import(/* webpackChunkName: "Landing" */ '../../pages/Landing/Landing'));
...

routes/keys.js

export default {
  Landing: '/',
 ...
};

above webpackChunkName matches appropriate page key from routes