Support more keybindings

**Is your feature request related to a problem? Please describe.**
The default keybind to confirm a commit when in the multi-line edit box is `` (alt/option + enter). This conflicts with the binding I use to spawn a new terminal on macOS (opt + enter).

**Describe the solution you'd like**
Be able to use different enter keybinds like `` for ctrl + enter. It seems that currently, no combinations with enter are possible according to https://github.com/jesseduffield/lazygit/blob/master/docs/keybindings/Custom_Keybindings.md

**Describe alternatives you've considered**
The current workaround is to use `` to switch back to the commit subject field and then submit by using ``, but it's not a great flow.

**Additional context**
If trying to set `` as the keybind in the config, `lazygit` crashes on startup with the error:

```
2025/02/12 18:03:34 Unrecognized key for keybinding. For permitted values see https://github.com/jesseduffield/lazygit/blob/master/docs/keybindings/Custom_Keybindings.md
```