Execute protoc from stencil CLI

[whoAbhishekSah]

Is your feature request related to a problem? Please describe.
We need to run protoc to generate a descriptor set. We can enhance Stencil CLI to do the job so that all things related to proto come under a single ecosystem of Stencil.

Describe the solution you'd like
We will enhance Stencil CLI to add one more command which will delegate the description set generation to protoc executable (which must be installed in the PATH)