Omit creating an event subscription if no event can be triggered

[saig0]

Description

• don't create an event subscription (i.e. an event trigger) for an activity if no event can be triggered (i.e. no boundary events)
• it is a preparation for Restore event subscriptions on replay #6200
• there is no test to verify that the subscription is not created because
  • currently, we don't have stream processor tests that verify the state directly
  • the impact is very low
  • it will be tested indirectly later when verifying the replay

Related issues

closes #6201

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 to the last two minor versions. You can trigger a backport by assigning labels (e.g. backport stable/0.25) to the PR, in case that fails you need to create backports manually.

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
• The change has been verified by a QA run
• The impact of the changes is verified by a benchmark

Documentation:

• The documentation is updated (e.g. BPMN reference, configuration, examples, get-started guides, etc.)
• New content is added to the release announcement

[korthout]

LGTM 🌮

[korthout]

On second thought, (after discussing): Please also do this for unsubscribe event

[saig0]

It would make sense to avoid the lookup if no events can be triggered. But it is not a trivial change (i.e. more refactoring required to make it work for interrupting event subprocesses). Since it would be an improvement to the current situation, we can postpone it for now 😅

[korthout]

Agreed, LGTM 🎉

[saig0]

bors r+

[ghost]

Build succeeded:

• continuous-integration/jenkins/branch