[OPT-4100] Add Camunda BPM 7.14 as supported version

Context:
As Camunda BPM 7.14 is scheduled for 13th of October 2020 Optimize 3.2 should support it officially as well.

AT:

7.14 is added to supported versions in docs and the EngineVersionChecker class
7.11 is dropped from supported versions in docs and the EngineVersionChecker class
new 7.14 & dropped 7.11 support are announced https://docs.camunda.org/enterprise/announcement/
dropped 7.11 support is noted in the upgrade guide
a dedicated 7.13 integration test step is added to https://ci.optimize.camunda.cloud/view/all/job/engine_compatibility/ (once 7.14 is released)
performance datasets are regenerated with 7.14 https://ci.optimize.camunda.cloud/view/all/job/generate-cambpm-test-data/

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