Tab completion not working in version 4.0.1 on macOS

## Description
When I start typing a statement, and pgcli suggests the complete statement in gray, and I just want to accept it, I try to hit Tab and instead focus the menu. I have to hit the right arrow key to select the suggested statement. This is strange compared to other editors.

Worse, sometimes hitting tab just cuts off what I'm typing.

## Desired Behavior
I would like to be able to use Tab to select the suggested statement. I can already use the down arrow to select the first completion menu item. I should at least be able to change this in the config file. There is no documentation about this.

However, there seems to be a lot of back-and-forth on keybindings and why we can't do this and that on keybindings in pgcli because of the way Python works, the library we're using, etc. which don't make sense to me as a developer, because the user should be able to configure these and not worry about hacking source just for keybindings. Please give us a documented way to change these without needing to edit source code.

## Your environment
macOS Sonoma 14.1.2 / Terminal / pgcli installed via homebrew

```
pip freeze main
altgraph @ file:///AppleInternal/Library/BuildRoots/dc12d579-7d9b-11ee-af04-6aecfccc70fe/Library/Caches/com.apple.xbs/Sources/python3/altgraph-0.17.2-py2.py3-none-any.whl
future @ file:///AppleInternal/Library/BuildRoots/dc12d579-7d9b-11ee-af04-6aecfccc70fe/Library/Caches/com.apple.xbs/Sources/python3/future-0.18.2-py3-none-any.whl
macholib @ file:///AppleInternal/Library/BuildRoots/dc12d579-7d9b-11ee-af04-6aecfccc70fe/Library/Caches/com.apple.xbs/Sources/python3/macholib-1.15.2-py2.py3-none-any.whl
six @ file:///AppleInternal/Library/BuildRoots/dc12d579-7d9b-11ee-af04-6aecfccc70fe/Library/Caches/com.apple.xbs/Sources/python3/six-1.15.0-py2.py3-none-any.whl
```