[v3-2-test] UI: Add per-searchbar 'Match anywhere' toggle for substring search (#66015)

[github-actions]

• UI: Add per-searchbar 'Match anywhere' toggle for substring search

Follow-up to #64963. The default search now uses the new prefix patterns
(*_prefix_pattern) for index-friendly lookups. Users who relied on
the prior substring behavior (*_pattern) can opt back in per
searchbar via a small regex-icon toggle.

Both surfaces support it:

• SearchBar — page-level inputs on Pools, Connections, Variables,
  Assets, Asset events, and Dags lists.
• FilterBar text pills — when supportsAdvancedSearch is set on
  the FilterConfig, the pill renders the toggle inline while editing
  and shows a regex indicator next to the value when collapsed. Wired
  on TaskInstances, DagRuns, Events, XCom, and HITL.

URL is intentionally untouched: shared links default to fast prefix
mode; toggle state is per-searchbar in localStorage
(advanced_search-<id>). The toggle uses onMouseDown +
preventDefault so clicking it inside a FilterPill does not collapse
the pill.

• Move toggle inside FilterPill input, drop warning palette

Address review feedback:

• Move the advanced-search toggle from a sibling next to the InputWithAddon
  to a real endAddon slot inside the same rounded box. The toggle now
  sits flush on the right of the pill input, mirroring the "Pool:" label on
  the left.
• Drop the colorPalette="warning" (orange) for the on state. Use the
  brand palette in both states; outline = off, solid = on. The UI doesn't
  use the warning palette much elsewhere, so this is more consistent.
• Move the toggle's tooltip strings (search.advanced.{title,description})
  from dags.json to common.json since the toggle renders on
  admin-namespace pages too. Drop the toggleAriaLabel translation key —
  aria-labels stay as plain English.
• Update 64963.significant.rst to point users at this opt-in toggle as
  the way back to the previous substring search behavior.

• Style FilterPill toggle as flush rounded addon

Make the toggle inside the FilterPill match the look of the "Pool:" label
on the left:

• Render as a Box-as-button with borderRightRadius="full" and
  alignSelf="stretch" so it fills the full pill height instead of
  being a tiny crushed icon centered in white space.
• Off state matches the label palette (gray.muted bg). On state uses the
  brand palette (solid bg, contrast fg).
• New variant="addon" | "standalone" on AdvancedSearchToggle.
  standalone keeps the previous IconButton look used next to the
  SearchBar; addon is the rounded right-side fill used inside
  InputWithAddon.
• Drop the pr={1} wrapper around InputWithAddon's endAddon so
  the addon abuts the pill's rounded edge.

• Rename newsfragment to 66015 and split into two parts

Move the user-visible note from 64963.significant.rst to a new
66015.significant.rst (this PR's number) and split it into two
paragraphs:

• The first paragraph references Update search parameters to better leverage DB indexes #64963 — the change from full-match
  *_pattern to index-friendly *_prefix_pattern.
• The second paragraph references UI: Add per-searchbar 'Match anywhere' toggle for substring search #66015 — the new per-searchbar
  "Match anywhere" toggle that lets users opt back into substring
  search.

• Trim newsfragment, drop localStorage/URL detail
  (cherry picked from commit d748835)

Co-authored-by: Pierre Jeambrun pierrejbrun@gmail.com