Remove unused span_status DB columns

[Ei-Sandi]

Description

This PR removes the span_status column from dag_run, task_instance and task_instance_history and associated SpanStatus enum. This field previously tracked OpenTelemetry span lifecycle state and is no longer needed after #62554.

Changes

• New Alembic migration dropping the column from all three tables (downgrade restores it with its original default)
• Removed the mapped column and imports from the DagRun, TaskInstance, and TaskInstanceHistory models
• Updated tests, coverage config, and migration references accordingly
• Fixed outdated file paths in the metadata database contributing docs

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Co-authored by: [Claude Opus 4.8] following the guidelines

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[xBis7]

@Ei-Sandi Thanks for the PR! I added 2 small comments.

Your branch seems to have conflicts, you need to do a rebase.

[xBis7]

It turns out that the sleep that was initially used for the span_status, now provides enough time for jaeger to pick up the spans. Removing it make the otel test flaky.

[xBis7]

LGTM!

[ashb]

Other than the version LGTM

[Ei-Sandi]

@ashb The version is updated, the merge conflicts are resolved, all the CI checks are passed. I think we can merge this now. Thank you.