Provide a representation of UI before actual content appears on the page

[Tarun-DXC]

Is your feature request related to a problem? Please describe.
While working on SOE for complex screen consisting multiple API calls, we get the feedback that performance is not good. During investigation it was identified that there are many API calls which happen on the screen. They are used to load different sections of screen. API response time is good but the screen is taking time to load because of multiple sections

Describe the solution you'd like
A temporary animation placeholder for when a service call takes time to return data and we don't want to block rendering the rest of the UI. e.g.
Shimmer on Fluent - https://developer.microsoft.com/en-us/fluentui#/controls/web/shimmer
Skeleton on Shopify - https://polaris.shopify.com/components/feedback-indicators/skeleton-page#navigation

Describe alternatives you've considered
None. Currently we use Spinner component to show ongoing API calls

Additional context
Add any other context or screenshots about the feature request here.

Add Labels
screen rendering, performance, assure policy