release-26.1: ui/cluster-ui: add optional headers to jobs/databases pages

[janmorales7]

Informs: CNSL-2186

Backport 1/1 commits from #169819.

/cc @cockroachdb/release

---

Make the page header optional via a showHeader prop on both JobsPage and DatabasesPageV2, allowing parent components to suppress the heading when embedding these pages in other layouts.

Move the "Auto stats collection" toggle from the PageHeader actions slot into the PageConfig filter bar on the databases page so it sits alongside other page-level controls.

A local stylesheet (databasesPageRoot.module.scss) is introduced to add margin-top: 10px on the content section below PageConfig. This compensates for the shared PageConfig container's margin-bottom: -10px (a sticky-header spacing trick) without modifying the shared stylesheet that affects 16+ pages.

Release justification: Add optional header support for embedded pages

[trunk-io]

😎 Merged successfully - details.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate.

[cockroach-teamcity]

This change is 

[dhartunian]

Two issues:

1. The isEmbedded prop on JobsPage has no default value. On master/26.2 the function component destructures it with isEmbedded = false, but here the class component accesses this.props.isEmbedded directly. It works by accident (!undefined === true) but should have an explicit default — either via static defaultProps or by destructuring in render. As-is it's fragile and inconsistent with the master implementation.

2. There's also a committed .pyc file in the 24.3 backport (#169868) — not this PR, but flagging since they're a set.

[janmorales7]

/trunk merge