[PBNTR-694] SkeletonLoading User Component and Filter Component doc examples

[ElisaShapiro]

What does this PR do? A clear and concise description with your runway ticket url.
PBNTR-694 requests the addition of two doc examples as outlined in the handoff here to the React SkeletonLoading beta kit - one demonstrating the use of the SkeletonLoading kit as an interim loading state for our User kit in two ways, the second for the Filter kit (also in two ways).

The goal for this kit is that using the SkeletonLoading kit and other code, we can mimic the shape of our other components and set a loading state for them accordingly. These doc examples demonstrate to devs how to use the SkeletonLoading kit + other Playbook kits as building blocks to construct loading interims.

This PR also contains a small update adding the correct Dark Mode styles to the containing cards in the Height & Width doc example (just needed to carry {...props} through). See third screenshot below.

Screenshots: Screenshots to visualize your addition/change
User Component doc example

Filter Component doc example

Height & Width doc example dark mode update

How to test? Steps to confirm the desired behavior:

1. Go to the SkeletonLoading kit page.
2. Scroll down to the User Component Example doc example, see two versions of the User kit in an interim loading state.
3. Scroll down to the Filter Component Example doc example, see two versions of the Filter kit in an interim loading state.

Checklist:

• LABELS Add a label: enhancement, bug, improvement, new kit, deprecated, or breaking. See Changelog & Labels for details.
• DEPLOY I have added the milano label to show I'm ready for a review.
  - [] TESTS I have added test coverage to my code.

[github-actions]

You merged this pr to master branch:
- Ruby Gem: 14.10.0.pre.rc.16
- NPM: 14.10.0-rc.16