feat(config): add deprecation warnings for legacy config fields (Phase 1: warnings in 2.x)

[re-vlad]

Description

Phase 1 of the deprecated config migration (non-breaking, target 2.1).

Logs console.warn when user config overrides still use legacy top-level fields:

• sslKeyPemPath without tls.key
• sslCertPemPath without tls.cert
• proxyUrl (deprecated and ignored at runtime)

Warnings are based on user overrides only (CONFIG_FILE), evaluated in loadFullConfiguration() before merge. Existing fallback behaviour from #1514 is unchanged.

Strict removal of these fields and startup failure for legacy-only configs remains planned for 3.0 (#1545).

Related Issue

Related to #1545 (Phase 1: warnings in 2.x; Phase 2: removal in 3.0).

Checklist

General

• I have read the CONTRIBUTING.md guidelines
• Commit messages follow Conventional Commits format
• I have a FINOS CLA on file

Documentation

• Documentation has been added/updated for any new features (N/A — warn-only, no user-facing config schema change)

Configuration

• If configuration schema (config.schema.json) was modified: (N/A — schema not changed)
  • TypeScript types regenerated (npm run generate-config-types)
  • Schema reference docs regenerated (npm run gen-schema-doc)

Tests

• Tests have been added/updated for new functionality
• Unit tests pass (npm test -- test/deprecatedFields.test.ts test/testConfig.test.ts)
• Linting and formatting pass (npm run lint on changed files)
• Type checks pass (npm run check-types) (or note: check-types:server if full check fails on unrelated local issues)

Test plan

• npm test -- test/deprecatedFields.test.ts
• npm test -- test/testConfig.test.ts (legacy TLS fallback still works; stderr shows expected warnings)
• npm run lint -- src/config/deprecatedFields.ts src/config/index.ts test/deprecatedFields.test.ts

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[codecov]

Codecov Report

❌ Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.87%. Comparing base (15c4495) to head (2ab6ad9).

Files with missing lines	Patch %	Lines
src/config/deprecatedFields.ts	80.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1626      +/-   ##
==========================================
+ Coverage   85.75%   85.87%   +0.11%     
==========================================
  Files          84       85       +1     
  Lines        8109     8128      +19     
  Branches     1376     1381       +5     
==========================================
+ Hits         6954     6980      +26     
+ Misses       1126     1120       -6     
+ Partials       29       28       -1     

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[re-vlad]

@kriswest can we add this proposition to agenda?

[jescalada]

LGTM - and seems fine to include in the 2.1 release 🚀