Based on the NieR: Automata wiki, the name YoRHa originated from a stage play under the same name, which became the foundation of the masterpiece of a game
What is "YoRHa"?
The storyline of "YoRHa" was the product of Yoko Taro. He collaborated with MONACA and DearStage among others to create a story that involves traditional Japanese idols who sing, dance, and later perform in the YoRHa stage play. This story later became the basis for the game NieR:Automata.
The YoRHa Stage Play is about the events that take place prior to NieR: Automata
Written by Yoko Taro, YoRHa is a stage play which tells of the events before NieR: Automata. Taking place in 11,941, it tells the story of the Pearl Harbor Descent Mission during the 14th Machine War
As to why "YoRHa" is capitalized the way it is, as stated in this interview (credits to reddit), Yoko Taro kept this a secret
Yoko: For NieR, it was just a design choice regarding the logo. I thought it felt a little light, which is why we decided to capitalize it. As for the YoRHa logo… that’s secret.