Add support for Chrome/Chromium browsers

[nilp0inter]

Preliminary tests indicate that AutoFirma works well with Chrome/Chromium; although it doesn't seem officially supported.

Thoroughly test the different modes under Chrome/Chromium, and add the option chromiumIntegration to both NixOS and Home-Manager modules.

[nilp0inter]

We are working on integrating AutoFirma with Chrome and Chromium-based browsers. This issue encompasses two key aspects:

1. Certificate Policy Challenge
   For the browser to communicate with AutoFirma via websocket/xhr, a custom certificate has to be registered first. This can be achieved using policies.
   Chrome/Chromium policies require certificates to be embedded as Base64-encoded strings rather than referencing file paths. The .pem certificate used by AutoFirma is generated outside the Nix store during runtime, making it inaccessible at build time. This complicates declarative configuration of Chrome policies to trust the AutoFirma web server.
   For comparison, Firefox policies can reference the .pem file directly, which aligns well with our current setup. This limitation in Chrome/Chromium requires further investigation to enable seamless integration.

2. Decoupling from Firefox's NSS Database
   By default, AutoFirma depends on the NSS database from Firefox as its truststore. However, AutoFirma can be configured to load truststores directly, including:

   • PKCS#11 modules for accessing smart cards.
   • .p12 files for loading certificates from disk.

   With these capabilities, it may be possible to configure AutoFirma for use with Chrome/Chromium without any dependency on Firefox. These changes have to be implemented as additional Home Manager configuration options.