CMR-11416: Update search proxy to use parameter store for lanes.json

[daniel-zamora]

Overview

What is the objective?

Allow the lanes configuration to be injected as an environment variable rather than requiring a JSON file on the container.

What are the changes?

Added CMR_PROXY_LANES_JSON environment variable support to ProxySettings. When set, its value is parsed directly as the lanes config JSON and takes precedence over CMR_PROXY_LANES_CONFIG (the file path). A structured settings_loaded log event was also added at startup to surface the active configuration (lanes, permits, toggles, backend URL, connection pool size) in CloudWatch. Some basic validation for the parameter store json value is also done.

What areas of the application does this impact?

The search proxy (search-proxy/). Specifically startup configuration loading. No changes to request handling, lane semaphore logic, or caching behavior.

Required Checklist

• New and existing unit and int tests pass locally and remotely
• clj-kondo has been run locally and all errors in changed files are corrected
• I have commented my code, particularly in hard-to-understand areas
• I have made changes to the documentation (if necessary)
• My changes generate no new warnings

Additional Checklist

• I have removed unnecessary/dead code and imports in files I have changed
• I have cleaned up integration tests by doing one or more of the following:
  • migrated any are2 tests to are3 in files I have changed
  • de-duped, consolidated, removed dead int tests
  • transformed applicable int tests into unit tests
  • reduced number of system state resets by updating fixtures. Ex) (use-fixtures :each (ingest/reset-fixture {})) to be :once instead of :each