Launching the GPU instance anytime when checking the performance guarantee off

**Is your feature request related to a problem? Please describe.**
As a student, GPU allocation has more priority than performance when running the Jupyter Notebook materials that include models such as GAN/Transformer in their lecture. The medium performance GPU is enough but running on CPU causes the delay of progress of the time limited lecture.

**Describe the solution you'd like**
The students can run GPU instance anytime if they turn on the performance not guarantee GPU checkbox when launching the GPU instance.

**Describe alternatives you've considered**
The students give up using Studio Lab and select other free notebook service that they can use GPU.

**Additional context**

This issue is from #92