feat: add gRPC trace demonstration

[michal-kazmierczak]

This PR adds trace demonstration of the gRPC instrumentation.

An example output:

❯ ruby trace_demonstration.rb
I, [2025-01-29T18:32:51.474157 #88063]  INFO -- : Instrumentation: OpenTelemetry::Instrumentation::Grpc was successfully installed with the following options {:allowed_metadata_headers=>[], :peer_service=>nil}
#<struct OpenTelemetry::SDK::Trace::SpanData
 name="proto.example.ExampleAPI/Example",
 kind=:client,
 status=
  #<OpenTelemetry::Trace::Status:0x0000000120f88678
   @code=1,
   @description="">,
 parent_span_id="\x00\x00\x00\x00\x00\x00\x00\x00",
 total_recorded_attributes=6,
 total_recorded_events=0,
 total_recorded_links=0,
 start_timestamp=1738171971478189000,
 end_timestamp=1738171971480708000,
 attributes=
  {"rpc.system"=>"grpc",
   "rpc.service"=>"proto.example.ExampleAPI",
   "rpc.method"=>"Example",
   "rpc.type"=>"request_response",
   "net.sock.peer.addr"=>"dns:///localhost:59320",
   "rpc.grpc.status_code"=>0},
 links=nil,
 events=nil,
 resource=
  #<OpenTelemetry::SDK::Resources::Resource:0x0000000120f830b0
   @attributes=
    {"service.name"=>"unknown_service",
     "process.pid"=>88063,
     "process.command"=>"trace_demonstration.rb",
     "process.runtime.name"=>"ruby",
     "process.runtime.version"=>"3.3.5",
     "process.runtime.description"=>
      "ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [arm64-darwin24]",
     "telemetry.sdk.name"=>"opentelemetry",
     "telemetry.sdk.language"=>"ruby",
     "telemetry.sdk.version"=>"1.6.0"}>,
 instrumentation_scope=
  #<struct OpenTelemetry::SDK::InstrumentationScope
   name="OpenTelemetry::Instrumentation::Grpc",
   version="0.2.0">,
 span_id="J\x1A\x04]\xC6`),",
 trace_id="\xCB\xAAza\x8A4,8s^\xF8$\xBB\x17\xBA\t",
 trace_flags=
  #<OpenTelemetry::Trace::TraceFlags:0x00000001201f13c0 @flags=1>,
 tracestate=
  #<OpenTelemetry::Trace::Tracestate:0x00000001051562f0 @hash={}>>