grpcsync: change refcounted utility to use value (#9303)

This PR changes the refcounted utility to take and store value instead
of a pointer to make sure we can simply store interfaces too.

This PR also changes 
- The usages of the refcounted utility for `HandshakeInfo` to use its
pointer for refcount.
- The signature of the refcounted route cluster
- Getting value for the ext proc client


RELEASE NOTES: None