Search bar: pressing ESC when the search bar is unfocused should not close the search bar

Hi there!

The original issue is that the search bar hides when I press the Escape key. It's not very useful when using Vim or tmux for example.

In this MR I added a new option "Hide search bar using Escape key". But default it's true.

Implementation is shown on the screenshot.

By the way, this is my first attempt to add something to this project. So I'm not familiar with how to contribute to KDE projects.

I will be grateful for any advice.

Thanks!