Fix some inconsistencies/bug with internal api

[nelsitoPuglisi]

Goal

Some internal API where writing the preferences service directly, instead of storing the value in-memory using metadata service.

Testing

Added some integration test to verify that still the preferences service is used when there is no value.

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 80.28%. Comparing base (457e4ee) to head (65715d6).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #571      +/-   ##
==========================================
+ Coverage   80.08%   80.28%   +0.19%     
==========================================
  Files         410      410              
  Lines       11048    11060      +12     
  Branches     1626     1627       +1     
==========================================
+ Hits         8848     8879      +31     
+ Misses       1549     1530      -19     
  Partials      651      651              

Files	Coverage Δ
...race/android/embracesdk/InternalInterfaceModule.kt	100.00% <100.00%> (ø)
...e/android/embracesdk/UnityInternalInterfaceImpl.kt	58.22% <100.00%> (ø)
...racesdk/capture/metadata/EmbraceMetadataService.kt	89.89% <100.00%> (+2.03%)	⬆️
...oid/embracesdk/capture/metadata/MetadataService.kt	100.00% <ø> (ø)
...oid/embracesdk/ReactNativeInternalInterfaceImpl.kt	64.44% <60.00%> (+2.22%)	⬆️

... and 3 files with indirect coverage changes

[bidetofevil]

LGTM. I want to refactor this so you don't have to pass the framework into the constructor and just use start(), but that'll be for later