Update instructions to install Drupal for FE using Umami demo data

[backlineint]

Closes #

Summary

The Pantheon Decoupled Umami Demo Profile was recently deprecated. This PR updates instructions to install Drupal for FE using Umami demo data using the main Umami install profile.

Dependencies and Timing

• Other prerequisites that must be completed before merging this PR

Release:

• [ X] When ready
• After date: $DATE

---

Post Launch

Do not remove - To be completed by the docs team upon merge:

• Redirect /old-path/ => /new-path/ (if applicable)
• Include/exclude pages ^ respectively within docs search service provider (if applicable)
• For Heroes - add a props post to the discussion board.
• Remove from the project board

[stevector]

Thanks @backlineint!