What is a single socket to ground-only plug adapter for electrical outlets called?
The plug used for grounding network equipment is different from the plug used for ESD protection, and they are NOT interchangeable.

ESD protection earth bonding points include integral current limiting resistance. Typically 1-10MegOhm. This is a safety feature. If you touch something live, it prevents significant live current flowing through you to the earth point, killing you.  It would not be legal to permit your employees to use a telecom ground bonding plug for that, and it would be stupid to do it to yourself.

A telecom/communications/network earth bonding point is a solid wire connection used to connect equipment to earth. This is sometimes done using a plug inside or adjacent to a networking cabinet. (It is more often done with a fixed grounding strap, or a three-pin plug also carrying power).