* config: introduce ExecSource value source
* auth: introduce OidcTokenSourceAuthProvider
* auth: use OidcTokenSourceAuthProvider if tokenSource config is present on the client
* cmd: allow exec token source only if CLI flag was passed
The ClientCommonConf, configuration file path, and server UDP port are
now passed around as arguments instead of being shared between
components as global variables. This allows for multiple clients to
exist in the same process, and allows client.Session to be used as a
library more easily.