Add prefetch disabling for specific Links

[krzysztof-pyrzyk-ah]

Description

I've added one more check before prefetch is being done so that it can be disabled easily.
This feature was working fine in React-Static v5, but in v6 there's a new router and it stopped working.

By adding prefetch="false" to a <Link> component we can prevent React-Static from prefetching this route.

Some documentation has to be added, but I wasn't sure where to put it.
Waiting for your suggestions.

Motivation and Context

Without this change you cannot disable prefetching specific links.
It fixes an issue I've opened here.

Types of changes

• Refactoring/add tests (refactoring or adding test which isn't a fix or add a feature)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• My changes have tests around them

[tannerlinsley]

Genius :)