Allow import and content hashes in index.html to allow cache busting

[dev-bjoern]

Is your proposal related to a problem?

I want my favicon (and other files in index.html) to be cache busted with content-hash in its name.
When I change my favicon it should be loaded not from cache.

Describe the solution you'd like

In index.html we do:
<link rel="icon" href="%PUBLIC_URL%/favicon.ico">

When the index.html is built, I want it to be converted to:
<link rel="icon" href="%PUBLIC_URL%/favicon.theHash.ico">.

We might need a special import syntax?:
<link rel="icon" href="___###import(../src/assets/favicon.ico)###___">.