Add document transformation capability for indexing

[tharropoulos]

TLDR

New options to transform Firestore documents before indexing to Typesense.

Change Summary

Added Configuration:

1. In extension.yaml:
   • Added 4 new configuration parameters:
     • TRANSFORM_FUNCTION_NAME: Name of Cloud Function for document transformation
     • TRANSFORM_FUNCTION_PROJECT_ID: Project where transform function is deployed
     • TRANSFORM_FUNCTION_REGION: Region of transform function
     • TRANSFORM_FUNCTION_SECRET: Auth secret for transform function

Added Functionality:

1. In utils.js:

   • Added transformDocument(): Calls external transform function with error handling
   • Implements fallback to original document when transformation fails

2. In indexOnWrite.js:

   • Updated to conditionally use document transformation before indexing
   • Added branch to handle transformed vs. non-transformed document flow

Added Tests:

1. New file test/utilsTransform.spec.js:

   • Tests for transform function with various scenarios:
     • Success path with proper transformation
     • Handling missing transform function configuration
     • Error handling for failed transformations
     • Edge cases like documents without IDs

2. In package.json:

   • Added new test command: test:utils

PR Checklist

• [x] I have read and signed the Contributor License Agreement.