fix(logql): correct OR filter behavior when one side is a TrueFilter

[Kim-Yukyung]

What this PR does / why we need it

This PR fixes incorrect OR behavior in LogQL line filters when one side contains an empty match. Previously, expressions such as {app="foo"} |= "notfound" or "" or regex patterns like (notfound|) incorrectly evaluated to false, even though the empty branch should act as a TrueFilter.

The fix updates newOrFilter so that the OR operation returns TrueFilter when either side is a TrueFilter, ensuring consistent and correct LogQL semantics.

Which issue(s) this PR fixes

Fixes #19523

Special notes for your reviewer

This change aligns OR filter behavior with how LogQL already treats empty string and empty regex branches individually ("" → TrueFilter). A small test was added to ensure empty-match OR behavior remains consistent going forward.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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