System information

• AutoDist version: 0.7.0
• Are you willing to contribute it (Yes/No): Yes

Describe the new feature and the current behavior/state
Add a BytePS strategy where CPU-only nodes are exclusively used for communication while GPU nodes for computation.

Will this change the current API? How?
This will add one more strategy and may add some functions to resource specs.

Describe alternatives you've considered
N/A

Additional context
N/A