Monitor List can say "no monitors found" while still loading

[justinkambic]

Describe the bug
We should check if the Monitor List component is still awaiting a server response before allowing the table's noItemsMessage to be "No uptime monitors found". If the query takes a long time (this happens to me when I put 100 items on the page at once), it will say there weren't any found and a couple of seconds later display the items.

To Reproduce
Steps to reproduce the behavior:

1. Configure 2+ heartbeat instances to watch 100+ monitors
2. Set the Monitor List's size to 100
3. Use the Uptime app's date picker refresh button
4. Observe the message shown in the table

Expected behavior
We want this message to indicate that the list is loading. This will require the creation of a new message to display in the translations folder.

There are cases where loading === true and we display a non-loading message:

[shahzad31]

i suspect this will be resolved once we merge elastic/kibana#66216

[justinkambic]

I'm about to review that, so if it's no longer an issue I'll add resolves keywords to that PR.

[shahzad31]

i believe this has been fixed in elastic/kibana#66216