fix: downloads path broken link in export(MAPCO-10645)

[almog8k]

Question	Answer
Bug fix	✔
Tests added	✔

This pull request refactors how file paths and URLs for export artifacts (GPKG and JSON files) are constructed and managed throughout the application. It introduces a new ArtifactPathBuilder utility class to centralize and standardize path building logic, removes hardcoded directory settings, updates configuration and Helm charts, and adapts the codebase and tests to use the new approach.

Key changes include:

Path and URL Management Refactor:

• Introduced the ArtifactPathBuilder class to encapsulate logic for building local file paths, S3 keys, and public download URLs for export artifacts, replacing direct path manipulation and hardcoded directory references. (src/utils/storage/artifactPathBuilder.ts)

• Updated ExportJobHandler to use ArtifactPathBuilder for all artifact path and URL construction, removing the use of the gpkgsRootDir config and direct path manipulation. (src/job/models/export/exportJobHandler.ts)
  Configuration and Helm Updates:

• Changed configuration files (config/default.json, config/custom-environment-variables.json, helm/values.yaml) to remove the obsolete gpkgsRootDir setting and introduce a structured storage.internalPvc config for mount paths and subpaths.

Testing Improvements:

• Added comprehensive unit tests for ArtifactPathBuilder to verify correct path and URL construction. (tests/unit/utils/artifactPathBuilder.spec.ts)
• Updated existing tests and mocks to align with the new path-building logic and configuration structure. (tests/unit/job/exportJobHandler/exportJobHandler.spec.ts, tests/unit/job/exportJobHandler/exportJobHandlerSetup.ts, tests/unit/mocks/configMock.ts)