Add parentRun alias to LineageEvent RunFacet to support older OpenLin…

[collado-mike]

Problem

Prior to https://github.com/OpenLineage/OpenLineage/pull/1037 , all Airflow OpenLineage events reported their parent runs as parentRun rather than the spec-defined parent facet. This change adds an alias to support those older events.

Unfortunately, jackson seems to prefer the alias field name rather than the target (or maybe it's ordered on some condition I don't understand), so if an event defines both, the parentRun facet will be used. This is confirmed in a unit test. The OpenLineage integration does use the same value for both parentRun and parent facets, so this should not cause any issues.

Note: All database schema changes require discussion. Please link the issue for context.

Checklist

• [X] You've signed-off your work
• [X] Your changes are accompanied by tests (if relevant)
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