Update About Us pages

[alinaboghiu]

What does this change?

Updates the content of the about us pages in line with requests from the board.

These were documented here: https://docs.google.com/document/d/1O4N2UcClX01X04yea6y6j5XRQjUHFgaqy4tkU-RPB9w/edit

The most significant changes are:

• updating the tab names from our organisation and history to Guardian Media Group and The Scott Trust respectively
• changing the links, images and some of the text on each page
• moving the guardian foundation section to the Scott Trust page

Fixes https://github.com/guardian/dotcom-rendering/issues/9594

New header:

Changes on the landing page

Changes on the Scott Trust page