Add a version field to TraceConfig

[panzhongxian]

Please add a version field to TraceConfig :

opencensus-proto/src/opencensus/proto/trace/v1/trace_config.proto

Lines 29 to 51 in 26aa36c

	message TraceConfig {
	// The global default sampler used to make decisions on span sampling.
	oneof sampler {
	ProbabilitySampler probability_sampler = 1;
	ConstantSampler constant_sampler = 2;
	RateLimitingSampler rate_limiting_sampler = 3;
	}
	// The global default max number of attributes per span.
	int64 max_number_of_attributes = 4;
	// The global default max number of annotation events per span.
	int64 max_number_of_annotations = 5;
	// The global default max number of message events per span.
	int64 max_number_of_message_events = 6;
	// The global default max number of link entries per span.
	int64 max_number_of_links = 7;
	}

Depending on a version filed in UpdatedLibraryConfig, Oc Agent will determine whether to send a UpdatedLibraryConfig back easily.

On library side, it's also helpful to determine whether they need to update the current libary config in there memory according to the Config response - UpdatedLibraryConfig.