[services] Tunnelbroker - Add skip authentication config parameter

Summary:
This diff introduces adding the sessions.skip_authentication config flag. It will be used in D6253 to skip the authentication mechanism.
As we don't have a function to get boolean flags from the config file (we have string parameters), the internal isParameterSet function was created to get the boolean value of the flag.

Linear task: ENG-2642

Test Plan: Adding the skip_authentication flag to the [sessions] section of the config file results in a true return from the isParameterSet('sessions.skip_authentication') function call.

Reviewers: jon, bartek

Reviewed By: jon

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D6251