Masthead - updates to support better logo layout

[mcoker]

Placeholder issue for https://github.com/patternfly/patternfly/pull/6870

So far this update will just be to add a new container around the masthead toggle and logo, and rename a couple of containers within it.

[srambach]

We've added a wrapper around the toggle and logo in the masthead. One wrinkle is that

• the name masthead__main was repurposed as the wrapper
• what was masthead__main is now masthead__brand
• what was masthead__brand is now masthead__logo

Old structure of the masthead was:

masthead
  masthead__toggle
  masthead__main
    masthead__brand
  masthead__content

New structure of the masthead is:

masthead
  masthead__main
    masthead__toggle
    masthead__brand
      masthead__logo
  masthead__content

[tlabaj]

closed by #10809