[EuiTour] Style and a11y fixes (#5225)

* [EuiTour] Made `subtitle` optional and fixed footer background
* [Breaking] Removes boolean as an option for `minWidth`
  And instead maps directly to `CSSProperties[‘minWidth’]` and applies it directly to `panelStyle`.
  Also adds `maxWidth` option.
* Better tests and switching to `h2` when no `subtitle`

CHANGELOG.md

@@ -1,6 +1,10 @@
 ## [`master`](https://github.com/elastic/eui/tree/master)
 
-No public interface changes since `38.2.0`.
+- Added `maxWidth` prop to `EuiTour`, made `subtitle` optional, and fixed heading levels and footer background ([#5225](https://github.com/elastic/eui/pull/5225))
+
+**Breaking changes**
+
+- Removed `boolean` from `EuiTour`'s `minWidth` type ([#5225](https://github.com/elastic/eui/pull/5225))
 
 ## [`38.2.0`](https://github.com/elastic/eui/tree/v38.2.0)
 

src-docs/src/views/tour/step.js

@@ -23,7 +23,7 @@ export default () => {
         step={1}
         stepsTotal={1}
         title="Title of the current step"
-        subtitle="Title of the full tour"
+        subtitle="Title of the full tour (optional)"
         anchorPosition="rightUp"
       >
         <EuiText>