Change default behavior to truncate Checks text from start when maxSize present

[sarahdeitke]

From these two tickets:

jenkinsci/github-checks-plugin#343 (comment)
jenkinsci/github-checks-plugin#423

We believe it is better to default truncating the checks text default behavior to be from the start rather than the end of the logs. This behavior is better because typically the most relevant logs, especially error logs, happen at the end of the output.

Testing done

Added two unit tests to cover the change, ensured that the unit tests passed

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[timja]

Thanks! Not tested manually but the unit test and by my reading of TruncatedString it looks good.