- Remove references to enterpriseSearchLayout CSS (which will be removed in an upcoming PR)

- Prefer to lean more heavily on default EuiPage props/CSS/etc.

- Handle conditional sidebar logic in this layout rather than passing it in as a prop

- Update props & DRY concerns to more closely match WorkplaceSearchPageTemplate
  - e.g. isLoading & pageChrome (mostly for document titles)
  - make FlashMessage and readOnlyMode work OOTB w/o props)

+ update PrivateSourcesSidebar to use EuiSIdeNav

- removing wrapping layouts, flash messages, chrome/telemetry

- Remove license callout, page header, and page chrome/telemetry

- NOTE: The early page isLoading behavior (lines 51-) is required to prevent a flash of a completely empty page (instead of preserving the layout/side nav while loading). We cannot let the page fall through to the route because some routes are conditionally rendered based on isCustomSource.

- FWIW: App Search has a similar isLoading early return with its Engine sub nav, and also a similar AnalyticsLayout for DRYing out repeated concerns/UI elements within Analytics subroutes.

- Mostly removing isLoading tests
- NOTE: Schema page could *possibly* use the new isEmptyState/emptyState page template props, but would need some layout reshuffling

- Opted to give these pages their own conditional layout logic - this could possibly be DRY'd out

- There is possibly extra cleanup here on this file that could have been done (e.g. empty state, titles, etc.) in light of the new templates - but I didn't want to spend extra time here and went with creating as few diffs as possible

…page templates

+ fix Link to EuiButtonTo on Organization Sources view

+ add related KibanaLogic branch coverage

…Sources pages

…crumbs

- `exact` is required to make the parent schemas/ not gobble schema/{errorId}

- added bonus breadcrumb for nicer schema navigation UX

- No tests need to update AFAICT