Add comments to explain TaskLogger#tail options (!6190) · Merge requests · GitLab.org / GitLab Development Kit

What does this MR do and why?

Adds doc comments to TaskLogger#tail explaining each keyword argument, as suggested in !4855 (comment 2512911293):

max_lines: caps the output and adds an "N lines omitted" notice with the path to the full log.
exclude_gems: drops lines containing /ruby/gems/ before the line cap, so gem backtraces don't crowd out application errors.
only_with_errors: returns nil when the log has no error-looking lines, so successful tasks produce no output.
smart_filter: selects lines by score (errors, warnings, and their neighbours) instead of taking the last N lines.

Also documents the return value (String, or nil when only_with_errors finds no errors). No behaviour change.

This MR has been reviewed against the MR acceptance checklist.
This contribution was prepared with the help of an AI assistant. I reviewed the changes and take responsibility for them.