Add default value for dataDir in init dataconnect

[joehan]

Description

Add default value for dataDir in init dataconnect, and makes it configurable via init emulators:dataconnect.

I intentionally held this back until post Thanksgiving freeze so that this persistence behavior is opt in for now.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 51.19%. Comparing base (a177fe0) to head (8468b5b).
Report is 42 commits behind head on master.

Files with missing lines	Patch %	Lines
src/init/features/dataconnect/index.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7989      +/-   ##
==========================================
- Coverage   51.36%   51.19%   -0.18%     
==========================================
  Files         422      423       +1     
  Lines       29344    29542     +198     
  Branches     5996     6031      +35     
==========================================
+ Hits        15074    15125      +51     
- Misses      12915    13057     +142     
- Partials     1355     1360       +5     

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