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

[dgp1130]

This is a v19 port of #33056.

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.

(cherry picked from commit 126b19b)

[gemini-code-assist]

Code Review

This pull request refactors environment options parsing and introduces support for the NG_TRUST_PROXY_HEADERS environment variable. However, the changes alter the behavior of allowedHosts by overriding programmatic options with environment variables instead of merging them, which could cause breaking changes. Additionally, NG_TRUST_PROXY_HEADERS should be updated to correctly parse boolean values ('true'/'false') instead of treating them as single-item string arrays.

[alan-agius4]

This PR was merged into the repository. The changes were merged into the following branches:

• 19.2.x: 2c0dfc2

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