Jump to first/last cell

### Problem

Could there be a keyboard shortcut to jump to the first/last cell?

I want to do this all the time (e.g. I am writing code in the last cell that I want to test, but I have all my imports in the first cell; I restart the kernel and have to scroll all the way to the top to run the first cell then all the way back to the bottom to run the last cell). I couldn't see a way of doing this currently, nor that anyone else had requested it.

Note that the current functionality of Home is not what I'm looking for - that shows you the first cell but the previously selected cell remains selected. You need to press Home and then reach for the mouse to click into the cell which is really annoying.

### Proposed Solution

A simple keyboard shortcut (e.g. Shift+Home/End) in escape mode to jump to the first/last cell. The first/last cell would then be selected (in escape mode).

### Additional context

I can't quite understand why this isn't already an option! It makes it almost impossible to use Jupyter notebook using just the keyboard which is what many users like to do!

No file or test is named in the issue. Start by locating Jupyter Notebook's keyboard shortcut handling and the escape-mode cell selection behavior; compare the existing Home behavior with the requested first/last-cell selection. Done means a keyboard shortcut jumps to and selects the first or last cell without requiring the mouse.

Written by the indexing model from the issue text.