UI: Refactor to use async/await syntax

[agilgur5]

Summary

Instead of using promises with many callbacks and chains, refactor to use the newer and cleaner async/await syntax where possible.

As mentioned in #11711

Use Cases

All UI logic that uses asynchronous promise chains

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[agilgur5]

A quick search on all appearances of .then in the UI showed mostly correct async code. There was one case that was parallelized and async with a render, but not sure if that was intentional or not (as it could potentially work fine that way). Some large chains though.

But the case of #11711 actually doesn't have a .then and a request could just end in a .get or .list etc, so that search above is a bit naive, but likely gets the majority of cases.