Add 5 tests for JWT allowed_connection_types enforcement which the
authenticator does not yet implement. Two tests (reject MQTT-only for
STANDARD context, reject unknown-only types) fail on assertions because
JwtAuthenticator currently ignores the claim. Three tests (allow
STANDARD, allow with unknown mixed in, case-insensitive match) pass
trivially since the field is not checked.
Also adds ConnectionType property to ClientAuthContext (defaults to
"STANDARD") so the tests compile.
