optional TLS on gRPC clients

[Zen Yui]

Is your feature request related to a problem? Please describe.
use case presented that requires secure gRPC connections from COS's gRPC clients.

Describe the solution you'd like
a boolean configuration for enabling TLS for the write side client and each read side client.

Describe alternatives you've considered
n/a

Additional context
this is to make COS work in the AWS ALB, which requires a secure connection for HTTP2/gRPC