Context:
As Camunda 7.16 gets released at the end of quarter 3 Optimize needs to officially support this new minor release while 7.13 support will be dropped

AT:

• Camunda Platform test version is raised to 7.16
• 7.15 is added to supported versions in the engine version checker
• Camunda Platform model version is raised to 7.16
• engine integration tests are extended with a 7.16 stage
• Supported Environment in docs are updated accordingly
• drop of support for 7.13 support
• removal of 7.13 engine integration test stage
• drop of support for 7.13 is listed in the update notes to 3.6.0

Hint:
see OPT-4972 on what to change