Firestore emulator exec should wait for import to complete before executing script

### [REQUIRED] Environment info

**firebase-tools:** 10.2.2

**Platform:** macOS

### [REQUIRED] Test case

It is too complicated to provide a test case because it requires uploading a lot of data. The issue is the following:
If you have a large import database (~0.5GB - this isn't even that big) then the emulator takes ~30s or so on my machine before I can 1) view the data in the emulator UI and 2) read/write to the DB. My requests to get or write documents just hang until this initialization is complete.

If you run emulator exec and then a script that writes to the DB, I am getting DEADLINE_EXCEEDED errors because the DB is not initialized yet as it is still processing the imported data.

### [REQUIRED] Steps to reproduce

See above

### [REQUIRED] Expected behavior

It should wait for the DB to finish initializing before running any exec script

### [REQUIRED] Actual behavior

DEADLINE_EXCEEDED error occurs because the script after emulator exec is trying to write to a document before the DB is initialize.

I confirmed that this is the issue by instead just starting the emulator in a separate terminal and then:
1. attempting to run the same script from the exec command immediately - it gives me a deadline exceeded error before i can view the data in the UI
2. attempting to run the same script from the exec command after the UI shows the data in the DB - the script runs fine and is able to read and write to the db