Add a new page into the new-session-dialog.

[agatha197]

Is your feature request related to a problem? Please describe.
There is an opinion that the number of sessions and the size of clusters are confusing.
So, I recommend you add a new page within the new-session-dialog and put those options on the new page.

Describe the solution you'd like
Make the structure of new-session-dialog as follows.

[1, 2 page]

• No change

[3 page]

• Resource Group
• Resource allocation
  • CPU
  • RAM
  • Shared Memory
  • GPU
  • Sessions
• Cluster mode
• Cluster size
• Session owner

[4 page]

• Advanced settings
  • Session owner
  • Sessions
  • OMP_NUM_THREAD* (with information dialog)

[5 page]

• Existing page 4
  (Total resource allocation, mounted folder, configurations, ...)

*OMP_NUM_THREAD
Backend.AI pre-specifies the OMP_NUM_THREADS environment variable as the number of allocated CPU cores in order to ensure that legacy software accurately recognizes container-allocated CPU resources while ensuring optimal performance when working with multi-threading through OpenMP. The pytorch official performance tuning guide also informs that it is necessary to adjust the value of OMP_NUM_THREAD when performing parallel operations as follows. https://pytorch.org/tutorials/recipes/recipes/tuning_guide.html#utilize-openmp

Describe alternatives you've considered
OMP_NUM_THREAD can actually be set in Environment Variable on page 1. I purposely added the OMP_NUM_THREAD option on page 4 because it seems likely that it often occurs when code for a distributed container environment is run on multiple cores within a single container. But you can add it wherever you think it is better.
So if you have a better idea to add the OMP_NUM_THREAD option to a better place, don't hesitate to share your ideas.

Additional context
You can save OMP_NUM_THREAD options like other environment variables on the first page.

[lizable]

Resolved via #1009.