fix: don't wait for actor being submitted

[romansmirnov]

Description

• Ensures that the activate jobs handler actor is submitted to the actor scheduler without blocking the actor thread
• This requires the usage of CompletableFuture to get notified when the handler has been scheduled successfully
• That way, the implementation works in case of an embedded and standalone gateway
• Adjust test cases to avoid potential race conditions

Related issues

closes #8992

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/1.3) 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
• If the PR changes how BPMN processes are validated (e.g. support new BPMN element) then the Camunda modeling team should be informed to adjust the BPMN linting.

[lenaschoenburg]

LGTM 👍 I'm glad that you wrote a test for this.

bors r+

[zeebe-bors-camunda]

Build failed:

• Run smoke tests on windows-2022

[lenaschoenburg]

bors retry

[zeebe-bors-camunda]

Build succeeded:

• Run smoke tests on ubuntu-latest
• Run smoke tests on windows-2022
• continuous-integration/jenkins/branch

[github-actions]

Backport failed for stable/1.2, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally.

git fetch origin stable/1.2
git worktree add -d .worktree/backport-8993-to-stable/1.2 origin/stable/1.2
cd .worktree/backport-8993-to-stable/1.2
git checkout -b backport-8993-to-stable/1.2
ancref=$(git merge-base d325919e7eef25f335c735088abb035dbfd58a8d 403942f036cdd9120d153f3f4b25cedd3d36fd13)
git cherry-pick -x $ancref..403942f036cdd9120d153f3f4b25cedd3d36fd13

[github-actions]

Backport failed for stable/1.3, because it was unable to create a new branch.

Please cherry-pick the changes locally.

git fetch origin stable/1.3
git worktree add -d .worktree/backport-8993-to-stable/1.3 origin/stable/1.3
cd .worktree/backport-8993-to-stable/1.3
git checkout -b backport-8993-to-stable/1.3
ancref=$(git merge-base d325919e7eef25f335c735088abb035dbfd58a8d 403942f036cdd9120d153f3f4b25cedd3d36fd13)
git cherry-pick -x $ancref..403942f036cdd9120d153f3f4b25cedd3d36fd13

[lenaschoenburg]

Apparently 1.2 does not have same bug. I wanted to just backport this PR but got a lot of conflicts (eg. EmbeddedGatewayServiceStep does not exist) so instead I just tried out the EmbeddedGatewayWithOneCpuThreadIT test on 1.2 and it passed 🤷