Add busy animation to Explorer

[jpellizzari]

Closes #3565

Adds a loading spinner and table animation for indicating a busy state. Notice the opacity getting reduced when filters/sorting gets changed:

screen-capture.46.webm

When responding to a query, we want to indicate to a user that the request is in progress. In environments with high Explorer request latency, we need to indicate that things are happening. Most environments respond in a matter of milliseconds, so we never needed this before.

Test with this to inject some fake latency:

---
 ui/src/hooks/query.ts | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/ui/src/hooks/query.ts b/ui/src/hooks/query.ts
index 77c0d8a6..5a0f64b8 100644
--- a/ui/src/hooks/query.ts
+++ b/ui/src/hooks/query.ts
@@ -66,7 +66,11 @@ export function useQueryService({
 
   return useQuery<QueryResponse, Error>(
     ['query', { terms, filters, limit, offset, orderBy, ascending }],
-    () => {
+    async () => {
+      await new Promise(accept => {
+        setTimeout(accept, 3000);
+      });
+
       return api.DoQuery({
         terms,
         filters: formatted,
-- 

[enekofb]

Approved after testing the expected behaviour: do not trust my UI review as always.