I am not able to hide/unhide the Launcher/Dash/Dock from the keyboard in Ubuntu 17.10 or in Ubuntu 18.04. Is it possible?
Not exactly what it's intended for, but you can use super+q to show the Ubuntu dock when it's hidden.
The actual use of the key combination is somewhat different, the super+q combination shows the dock with numbers next to each icon in the dock. Then you release q and press the number to launch or switch to the associated application.
If this feature is disabled, run the following to enable it first:
gsettings set org.gnome.shell.extensions.dash-to-dock hot-keys true
If you wish to hide/unhide on the go, the following extension does it.
It has a button in the top bar.
See the Gnome extension Dock Hide Button by sanjarcode.