Backfill function attempts to rerun admin.initializeApp on rerun

I ran backfill, had to fix a schema issue (preventing backfill from making updates) and re-ran backfill soon after.

Firebase Functions logs shows this error:

Error: The default Firebase app already exists. This means you called initializeApp() more than once without providing an app name as the second argument. In most cases you only need to call initializeApp() once. But if you do want to initialize multiple apps, pass a second argument to initializeApp() to give each app a unique name.
    at FirebaseAppError.FirebaseError [as constructor] (/workspace/node_modules/firebase-admin/lib/utils/error.js:44:28)
    at FirebaseAppError.PrefixedFirebaseError [as constructor] (/workspace/node_modules/firebase-admin/lib/utils/error.js:90:28)
    at new FirebaseAppError (/workspace/node_modules/firebase-admin/lib/utils/error.js:125:28)
    at FirebaseNamespaceInternals.initializeApp (/workspace/node_modules/firebase-admin/lib/firebase-namespace.js:65:23)
    at FirebaseNamespace.initializeApp (/workspace/node_modules/firebase-admin/lib/firebase-namespace.js:371:30)
    at /workspace/src/backfillToTypesenseFromFirestore.js:29:13
    at cloudFunction (/workspace/node_modules/firebase-functions/lib/cloud-functions.js:134:23)
    at /layers/google.nodejs.functions-framework/functions-framework/node_modules/@google-cloud/functions-framework/build/src/invoker.js:199:28
    at processTicksAndRejections (internal/process/task_queues.js:95:5)

Firebase functions can be re-used so admin.initializeApp ends up being called multiple times.

Submitting a PR here: https://github.com/typesense/firestore-typesense-search/pull/5

typesense / firestore-typesense-search

Backfill function attempts to rerun admin.initializeApp on rerun #6