SLING-13050 Include Integration Tests

[stefanseifert]

we want to move the integration tests form the separate github repo
https://github.com/apache/sling-org-apache-sling-models-integration-tests
into the main code repo, to make sure the ITs are executed on each code change.

integration tests are migrated to Sling Starter 14 and feature launcher.

this PR introduces a structure of modules instead of the single "impl" bundle:

reactor
   +-- parent
   +-- impl
   +-- it/test-models
   +-- it/integration-tests

this also adds a new integration test case using jakarta serlvet API.

[sonarqubecloud]

Quality Gate failed

Failed conditions
76.8% Coverage on New Code (required ≥ 80%)
C Reliability Rating on New Code (required ≥ A)

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