I had deleted the Google keyboard app and was using a third party keyboard app on my Motorola Nexus 6. Just now, I hard reset my phone and come to know that there is no default keyboard installed; making me unable to pass through the setup wizard. I am running Android 5.1.1 and because of factory reset protection, it's a must to pass through setup wizard, can't skip anything. Please help me fix this, thanks in advance.
Because you are currently in an unknown state, the "best" option here is to reflash the factory images manually. Google provides factory images and instruction on their Factory Images for Nexus Devices page, and you could also upgrade to 6.0.1 if you wanted to.
Going through this procedure will return your Nexus device to it's factory condition, except with the version of software you chose to install.