Set a question mark icon in background tab when user input is required in there

## Prerequisites
- [X] I have searched open and closed issues for duplicates.

## Feature
When you're having one tab open, running a bash script installing a lot of packages via apt and in the next line it requires user input like this:

```
read -p "Execute operation? yes/no: " answer

if [ $answer == "yes" ]; then
other-long-running-operation?
fi
```
I would usually do other tasks while the packages are installed so most of the times, I open a new terminal and do work in there. Then the script reaches a point where it requires user input before it can continue. I want to be informed that the script is waiting so I don't assume it's finished, then shutdown my computer and realize that it didn't finish when I'm already on train with no Wifi.

**Describe the solution you'd like**
The tab that is not active and reaches a line where user input is required, should have a question mark icon next to it's title (preferrebly a blue, round icon with white outer border and white question mark in the middle).

**Existing work**
Green check icon is displayed when a command exits with return code 0 in a background tab, red exclamation mark when the result was != 0.

**Describe alternatives you've considered**
Can't think of any at the moment.

**Additional context**
Fresh install of elementaryOS 5.1