[processor/transform] Optimize the use of trace_state in condition

[ralphgj]

Is your feature request related to a problem? Please describe.
In open-telemetry spec, trace_state is a key-valued struct. Now trace_state seems being used as a string in a condition. Maybe we can make it easier to use.

Describe the solution you'd like
In example, when trace_state having the value of key1=val1,key2=val2 in spans, we can give a query configuration like this:
set(status.code, 1) where trace_state["key1"] == "val1"

[codeboten]

@ralphgj any chance you'll be able to help with this one since you've already submitted another trace state related PR?

[ralphgj]

Of course, I will take a try.

[TylerHelmuth]

I believe you'll need to add a new accessor function and reuse the logic that attributes uses for key access.