Description 📝

As a follow up to #9704, I noticed a few issues and room for improving the visual loading pattern (long query, prefetching issue, multiple circular loaders).

Apart from the prefetching issue, this PR offers improvements as a proof of concept to visually help the user while the page is loading. Those changes will be submitted to UX as well for approval.

Major Changes 🔄

• Fixes the prefetching pattern from the navbar (was fetching twice: once from menu entry hover prefetch, twice when navigating to the page). There should be only one request.
• Adds a clearable field to the App Search textfield. Small improvement but mirror the Category selection next to it and makes it easier to get the full list back
• Replace the second circular loading pattern with our skeleton loader (App grid). Two circular loaders is not very friendly and seems to indicate something is wrong. Using the skeletons helps pre-shaping the content while announcing categories early (previously obfuscated by the loader)
• Adds a "fake" loading percentage to the search bar. This is more the POC part. The code is commented but the gist of it is to provide an indication to the user this request will take longer (it is an anomaly within CM). While not being based on a true API roundtrip, I believe it to be helpful and potentially relieve some frustration waiting for the request to complete. All in all it is an inoffensive distraction pattern. The value of the counter is based on an average API response time. Note: whatever we do with it the util could be useful for other purposes.

Preview 📷

Before	After

How to test 🧪

Requisites: pull code locally

Refetching fix

1. While you network console is open (and use a XHR "strackscript" filter), navigate to /linodes - should notice no request
2. Hover "Marketplace" - notice one request
3. Click on "Marketplace" - notice no new request
4. Reload Marketplace page - notice one request
5. Navigate through site and come back to Marketplace - no new request and data should be loaded immediately
6. You can also verify other scenari: hover over item for 4s then click, request should take about half time when landing on the marketplace page

Compare this behaviours with production and confirm fix + no regression

Visual fixes

1. Use search and confirm filtering and clearing filtering
2. Assert percentage count is not too far off (it may be if on a very slow connection)
3. Confirm experience is isn't degraded, if not bettered by these changes