feat(push): add callback on subscription lost event

[cromoteca]

This PR allows to define a behavior for when the reopened event happens on the client.

The new onSubscriptionLost callback can be used to perform an action when the websocket is reopened, but there's no longer a Flux connected to the subscription. Based on the return value of that callback, automatic resubscription can be performed.

Fixes #2716

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 94.48%. Comparing base (ec4ba7f) to head (c18d859).

Files with missing lines	Patch %	Lines
packages/ts/frontend/src/FluxConnection.ts	83.33%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2737      +/-   ##
==========================================
- Coverage   94.53%   94.48%   -0.05%     
==========================================
  Files          81       81              
  Lines        2635     2648      +13     
  Branches      664      666       +2     
==========================================
+ Hits         2491     2502      +11     
- Misses        140      142       +2     
  Partials        4        4              

Flag	Coverage Δ
unittests	94.48% <83.33%> (-0.05%)	⬇️

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[sonarcloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud