Show one loading indicator with placeholder for all cards on the add page

Origin description

When you try to load the Add page, all the options from the load page do not come together. Some options come earlier than other.

I found this issue on Chrome browser with Version 78.0.3904.108 and I am using 4.3.0-0.nightly-2019-12-10-034925 build for testing. 

Please have a look at the shared video.

Description

As a user I don't want a flickering (or at least less flicking) add page if many operators are installed.

Acceptance Criteria

1. Show a loading indicator with placeholders when there are pending fetches if a operator is installed or if the user has the right permissions to select an add option. Based on a previous discussion on the Add page redesign epic we expect that one loading indicator is fine and that we can show all add pages together.
2. Handle the case when a fetch calls breaks or runs too long. For example show the already loaded items after 2 second anyway?!
3. Please list add card actions with some measurements how long it takes until they could be rendered.
4. Update the unit tests and add tests for successfully, failed and timeouted fetches.

Additional Details:

1. Start work after the redesign of this component in ODC-5561
2. See also PatternFly Skeleton component https://www.patternfly.org/v4/components/skeleton