JENKINS-65970 Ability to ignore indexing errors and continue scanning

[sfosterdw]

Description

A brief summary describing the changes in this pull request. See
JENKINS-65970 for further information.

The linked issue is about a specific case where this plugin is looking for a Jenkinsfile in a path which is a submodule root for a given SCMHead. Jackson tries to deserialize the response as an array and fails because a single submodule result is returned, which is also not currently handled in the github-api library. I tried to figure out what would be required to cover that case and found some discussion about needing submodule traversal support to properly handle it hub4j/github-api#915.

One option is ignoring the specific MismatchedInputException in the GitHubSCMProbe.stat function which retrieves the contents of a directory, but that didn't seem great. I left it commented out in the draft.

I then saw that there was some error-ignoring logic for Pull Request heads already which had a comment implying the rationale behind interrupting scanning except in this case. I think there are probably cases where a user doesn't mind ignoring most errors and would rather complete the indexing job. I tried to implement similar error-ignoring logic for the other SCMHead types on an opt-in basis.

I'm opening this PR for solution discussion as well as reviews of this implementation.
Not much of a java developer so any pointers are appreciated :)

Submitter checklist

• Link to JIRA ticket in description, if appropriate.
• Change is code complete and matches issue description
• Automated tests have been added to exercise the changes
• Reviewer's manual test instructions provided in PR description. See Reviewer's first task below.

Reviewer checklist

• Run the changes and verify that the change matches the issue description
• Reviewed the code
• Verified that the appropriate tests have been written or valid explanation given

Documentation changes

• Link to jenkins.io PR, or an explanation for why no doc changes are needed

Users/aliases to notify