[services] Tunnelbroker - Requests SessionID format validation.

Summary:
Check the session format validity in the gRPC request handler using the simple validate function, as we have for deviceID in D2978

Related linear task ENG-650

*Dependencies:*
Depends on D3124

Test Plan:
Sent valid format of UUID and got true.
Sent wrong format of UUID and got false.

Reviewers: palys-swm, karol-bisztyga, ashoat, jimpo

Reviewed By: palys-swm, karol-bisztyga, ashoat

Subscribers: benschac, ashoat, palys-swm, Adrian, atul, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3113