sessionstore: Add flag to disable TLS support
The raison d'etre for this the collection of profile information in
the staging environment ala go tool pprof. Recent versions of the
tooling support specification of the ca, cert, and key when connecting
to a debug endpoint, but the version currently installed on deploy
hosts does not.
Having this option accidentally enabled in production would be Bad™;
We may want to consider reverting this after T229697 is closed.