[Feat] docs: Design synchronization

[cwhite911]

This issue is meant to track the progress of synchronizing the branding adopted by the PSC in PR OSGeo/grass-website#506 with the MkDocs documentation and to formalize the page layout designs to be applied both the GRASS website and GRASS tutorial sites.

The reasoning for doing this here instead of in the grass-website repo (PR OSGeo/grass-website#506) is because MkDocs provides a consistent structure to build from. The GRASS website has a lot a variation between pages which makes it harder to do a quick and comprehensive change.

The goal of this PR is to use the new docs as the template to update both the website layouts/templates and the tutorials providing all of the GRASS sites a consistent look and feel.

For these changes I am breaking them up into smaller PRs.

• docs: synchronizing brand colors #5578
• docs: Synchronize MkDocs styles with brand #5586
• docs: adding new logo to docs #5612