Fix env overrides for optional scalar config values

[preko-p]

References

• Fixes Environment variable overrides are ignored if default setting is empty #5279

Description

Environment variable overrides only walked config keys that were already present and non-empty in the merged config object. Valid optional scalar config settings with empty or absent defaults, such as matomo.trackerUrl and rest.ssrBaseUrl, could therefore ignore their corresponding DSPACE_* environment variables unless a placeholder default was added.

This PR extracts the environment override logic into a focused helper and adds a bounded supplemental map for optional scalar config leaves that cannot be discovered by the runtime object walk.

Instructions for Reviewers

List of changes in this PR:

• Preserves the existing recursive environment override behavior for populated scalar config leaves.
• Adds supplemental scalar environment overrides for:
  • matomo.trackerUrl via DSPACE_MATOMO_TRACKERURL
  • rest.baseUrl via DSPACE_REST_BASEURL
  • rest.ssrBaseUrl via DSPACE_REST_SSRBASEURL
• Keeps the existing non-convention DSPACE_REST_SSRBASEURL handling in config.server.ts for compatibility.
• Avoids adding placeholder defaults to DefaultAppConfig.
• Avoids reverse-parsing environment variable names.
• Does not add array/object environment parsing.
• Documents that future absent/empty optional scalar config leaves require an explicit supplemental-map entry.
• Adds focused tests for:
  • derived DSPACE_* names;
  • absent and empty optional scalar overrides;
  • existing number/boolean/string conversion behavior;
  • empty environment values remaining non-overrides;
  • server-only values being stripped from client config output;
  • non-object parents not being clobbered by future supplemental entries.

Scope note: this is intentionally a scalar-only fix for optional config leaves that cannot be discovered from the runtime object shape. It does not attempt to infer TypeScript interfaces at runtime or parse arrays/objects from environment variables.

Verification performed locally with Node v22.17.1 and npm@10.9.4:

npx -y npm@10.9.4 clean-install
npx -y npm@10.9.4 run test:headless -- --include src/config/env-config-overrides.spec.ts
npx -y npm@10.9.4 run lint -- --quiet
npx -y npm@10.9.4 run check-circ-deps
git diff --check

Results:

• Focused config override spec: 7 SUCCESS
• Lint: 0 errors with existing repo-wide warnings
• Circular dependency check: no circular dependencies found
• git diff --check: no whitespace errors

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes ESLint validation using npm run lint
• My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR includes new/updated focused specs for the changed behavior. Local verification ran the focused config spec, lint, and circular dependency check; the full suite is deferred to CI.
• My PR aligns with Accessibility guidelines if it makes changes to the user interface.
• My PR uses i18n (internationalization) keys instead of hardcoded English text, to allow for translations.
• My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.
• If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.