display snackbar when app update is available

[fremartini]

closes #335

[ghost]

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[codecov]

Codecov Report

Attention: 124 lines in your changes are missing coverage. Please review.

Comparison is base (ed05b24) 72.36% compared to head (9045e1d) 67.75%.

Files	Patch %	Lines
...ures/upgrader/data/datasources/play_store_api.dart	0.00%	69 Missing ⚠️
...tures/upgrader/data/datasources/app_store_api.dart	0.00%	43 Missing ⚠️
lib/core/external/platform_service.dart	0.00%	5 Missing ⚠️
.../purchase/data/repositories/mobilepay_service.dart	0.00%	5 Missing ⚠️
...es/upgrader/presentation/cubit/upgrader_state.dart	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #559      +/-   ##
==========================================
- Coverage   72.36%   67.75%   -4.61%     
==========================================
  Files         133      139       +6     
  Lines        1603     1743     +140     
==========================================
+ Hits         1160     1181      +21     
- Misses        443      562     +119     

Flag	Coverage Δ
unittests	67.75% <14.48%> (-4.61%)	⬇️

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