fix: add support for java8 date time in signals

[taefi]

Description

This introduces endpointObjectMapper bean to be used in both the EndpointInvoker and in the Signals library.
If the user overrides the JacksonObjectMapperFactory by the EndpointController.ENDPOINT_MAPPER_FACTORY_BEAN_QUALIFIER qualifier, it also by default affects the the object mapper in the signals library.

Fixes #2891

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.70%. Comparing base (1636cb7) to head (da2d444).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2899   +/-   ##
=======================================
  Coverage   92.70%   92.70%           
=======================================
  Files          83       83           
  Lines        2851     2851           
  Branches      739      739           
=======================================
  Hits         2643     2643           
  Misses        157      157           
  Partials       51       51           

Flag	Coverage Δ
unittests	92.70% <ø> (ø)

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

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

See analysis details on SonarQube Cloud

[cromoteca]

Isn't it dangerous to define a public api to set the mapper? Can package-level be enough for testing?

[taefi]

Well, not all of the test classes in the same package. And, I'm not sure whether we can impose such a limitation to user codes.