libwebsockets

ss: add static policy as a build option

In some cases devices may be too constrained to handle JSON policies but still
want to use SS apis and methodology.

This introduces an off-by-default cmake option LWS_WITH_SECURE_STREAMS_STATIC_POLICY_ONLY,
if enabled the JSON parsing part is excluded and it's assumed the user code
provides its policy as hardcoded policy structs.