Create atomics support and config

This commit adds support for enabling and serving the PartyTown Atomics library. There is a new config option that enables this behavior, and users can activate it using the PartyTown settings UI. When activated, the server will deliver the partytown-atomics.js file, and will serve all HTTP requests with two new HTTP headers:

Cross-Origin-Embedder-Policy: credentialless
Cross-Origin-Opener-Policy: same-origin

These are required for the Atomics library to work. When a client's browser doesn't support atomics, Partytown will detect this and fall back to the default experience.

I've done some testing to ensure that the atomics library can mount to the page, and that partytown-enabled scripts still work using this method. Eveything looked good on my end.

The atomics support option is disabled by default, leaving it up to server admins to turn it on as desired. The settings form description also directs them to the official docs, so they can learn about the implications if this feature.