deps: bump zeebe version to 8.1.20

[npepinpe]

Description

Bumps Zeebe to 8.1.20 for stable/8.1

Definition of Done

Not all items need to be done depending on the issue and the pull request.

Code changes:

• The changes are backwards compatibility with previous versions
• If it fixes a bug then PRs are created to backport the fix

Testing:

• There are unit/integration tests that verify all acceptance criterias of the issue
• New tests are written to ensure backwards compatibility with further versions
• The behavior is tested manually

Documentation:

• Javadoc has been written
• The documentation is updated