Remove RaftLogReader#isEmpty

[npepinpe]

Description

This PR removes RaftLogReader#isEmpty in order to simplify #6307. It removes the call to check if the journal is empty and simply scans the log for ZeebeEntry. This is a naive implementation which may be slow, however in practice the log is made up of mostly ZeebeEntry, or it's empty - in which case it should return fairly quickly.

Related issues

related to #6307

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

[npepinpe]

Ah, wait, this PR is based on a different branch. Let me rebase before you review.

[MiguelPires]

This doesn't remove isEmpty from the JournalReader and all its implementations. Is there a reason you're keeping those?

[npepinpe]

Right now to keep the PR small and focused, as it seemed a bit out of scope for me - I would like to challenge the use of isEmpty and any other "unnecessary" APIs after #6307 as clean up tasks.

[MiguelPires]

bors r+

[ghost]

Build succeeded:

• continuous-integration/jenkins/branch