Add date and value filters to Backfills UI API

[Phinhas214]

Related: #53049

Add date and value filters to the Backfills tab UI.

Adds 6 of the 8 filters requested in #53049 to the Backfills tab: start_date, end_date,
created_at, completed_at, reprocess_behavior, and max_active_runs.
The remaining 2 filters duration and status are deliberately left out see "Open questions for reviewers" below.

Before

After

backfill_filters_recording.mov

Open questions for reviewers

duration

• Motivation: Surfaces long-running backfills that may impact system performance
• Backfill has no duration column. DagRun derives its duration from
  end_date - start_date via a dialect-aware hybrid_property, but Backfill has neither of
  those columns. The closest fields are created_at/completed_at. Mirroring DagRun's pattern directly on those fields means a running
  backfill has completed_at = NULL, so duration IS NULL, and NULL fails any SQL
  comparison. This implementation would silently exclude every
  currently running backfill, even though "surface long-running backfills" (the motivation for duration filter) should include ones still running in my opinon.
• One option: compute duration as
  now() - created_at when completed_at IS NULL, so in-progress backfills still get a
  duration value. Would you like me to implement it that way, or handle it differently?

status

• Motivation: Surface failed or incomplete backfills
• similarly, Backfill has no status column — only is_paused and
  completed_at. list_backfills_ui already has a partial precedent (active, based on
  completed_at IS NULL) but this definition of status would only give us running vs. finished states.
• Should status build on that directly, or does it need to look at
  associated DagRun states (e.g: join out to child DagRun states to support "failed" state?)

Happy to follow up on duration/status once there's a direction.

---

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Generated-by: Claude Code (Sonnet 5) following the guidelines

[boring-cyborg]

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[Phinhas214]

• start_date/end_date are exposed as public filter names, but Backfill has no columns
  with those literal names. The underlying columns are from_date/to_date.
• Used
  datetime_range_filter_factory's attribute_name argument to map the public-facing name to
  the real column, so the API surface matches what DagRun already exposes without renaming
  Backfill's columns.

[Phinhas214]

max_active_runs is implemented as a RangeFilter (via float_range_filter_factory) rather
than an exact-match FilterParam, since the issue frames it as diagnosing throttling
("more/fewer than N active runs"), which a range serves better than exact equality.