Logging & Error Handling improvements

[mkurapov]

Context

We do not log a whole lot of things right now, which makes it hard to debug. Furthermore, we want to make Rafiki ready to work with log management in the future. So let's add some logs!

More is more, we can always get rid of logs later. Add logs wherever you would want to see them.

Todos

• [x] #1905
• [ ] #2575
• [x] #2574
• [ ] #2576
• [x] #2577
• [x] #2578
• [x] #2579
• [x] #2580
• [x] #2581
• [x] #2582