Apply Global Labels for self instrumentation when provided

[kyungeunni]

APM Server can be self-instrumented and when in managed mode, the configuration for the self-instrumentation contains more than what it's supported by the instrumentation package from libbeat, which APM Server currently rely on.
Missing configs are namely TLS and global labels.

This can potentially confuse users if they have specified such missing configs and it doesn't take place(missing global labels in traces, TLS config not applied in HTTP client etc.)

We should support all the configs that is sent by Elastic Agent, and for that we might want to consider having our implementation rather than making changes to libbeat to reduce our dependency on libbeat.

related ticket: #11381 (comment)