fix(@angular/ssr): add support for configuring trusted proxy headers via environment variable

Adds support for configuring trusted proxy headers via the `NG_TRUST_PROXY_HEADERS` environment variable in `AngularNodeAppEngine`.
This allows users to specify which proxy headers (such as `X-Forwarded-Host`) should be trusted when running the server-side application behind a reverse proxy, without needing to modify the application code. The environment variable accepts a comma-separated list of header names.
If the `NG_TRUST_PROXY_HEADERS` environment variable is set and contains non-empty values, it will take precedence over the `trustProxyHeaders` option provided programmatically in the `AngularNodeAppEngine` constructor options.