fix: ignore unknown extension elements

[menski]

Description

Allow users to deploy BPMN models with unknown extension elements added by other vendors to allow round-trips and migrations.

Related issues

closes #4817

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.

Please refer to our review guidelines.

[github-actions]

Test Results

   804 files  ±    0     804 suites  +1   1h 36m 21s ⏱️ - 6m 28s
6 321 tests +191  6 312 ✔️ +191  9 💤 ±0  0 ❌ ±0 
6 507 runs  +191  6 498 ✔️ +191  9 💤 ±0  0 ❌ ±0 

Results for commit c3aee33. ± Comparison against base commit 0e6c55d.

♻️ This comment has been updated with latest results.

[saig0]

@menski nice 👍 Thank you for fixing the issue 🎉

[saig0]

bors merge

[zeebe-bors-camunda]

Build succeeded:

• Java checks
• Test summary
• Go linting