#418: add customFilterDropdown Prop

[ethanluc7]

Related to issue: #418

Summary

adds customFilterDropdown prop that allows for extra drop downs to be added and used to filter within the DictionaryViewerPage component.

Description of Changes

• Added CustomFilterDropdown, DictionaryTableViewerProps, and ToolbarCustomDropdown types, plus a getByDotPath helper to resolve nested property paths on schema objects to DictionaryTableViewer.tsx
• Extended getFilteredSchema to accept active custom filters. Schemas that don't match selected filter values are excluded entirely (returns null). Shows an empty-state message when no schemas match.
• Scans all schemas to collect unique values for each custom filter property, builds dropdown options dynamically, and manages selection state via customFilterSelections.
• Renders a for each custom filter in the toolbar, with an "All" option to clear the filter in Toolbar.tsx

Readiness Checklist

• Self Review
  • I have performed a self review of code
  • I have run the application locally and manually tested the feature
  • I have checked all updates to correct typos and misspellings
• Formatting
  • Code follows the project style guide
  • Automated code formatters (ie. Prettier) have been run
• Local Testing
  • Successfully built all packages locally
  • Successfully ran all test suites, all unit and integration tests pass
• Updated Tests
  • Unit and integration tests have been added that describe the bug that was fixed or the features that were added
• Documentation
  • All new environment variables added to .env.schema file and documented in the README
  • All changes to server HTTP endpoints have open-api documentation
  • All new functions exported from their module have TSDoc comment documentation