Add tracing configuration variables

[joshblakeley]

list of zipkin configuration env variables
TYK_GW_TRACER_OPTIONS_REPORTER_URL TYK_GW_TRACER_OPTIONS_REPORTER_BATCHSIZE TYK_GW_TRACER_OPTIONS_REPORTER_MAXBACKLOG TYK_GW_TRACER_OPTIONS_SAMPLER_NAME TYK_GW_TRACER_OPTIONS_SAMPLER_RATE TYK_GW_TRACER_OPTIONS_SAMPLER_SALT TYK_GW_TRACER_OPTIONS_SAMPLER_MOD

List of jaeger configuration env vars
TYK_GW_TRACER_OPTIONS_SERVICENAME TYK_GW_TRACER_OPTIONS_DISABLED TYK_GW_TRACER_OPTIONS_RPCMETRICS TYK_GW_TRACER_OPTIONS_TAGS TYK_GW_TRACER_OPTIONS_SAMPLER_TYPE TYK_GW_TRACER_OPTIONS_SAMPLER_PARAM TYK_GW_TRACER_OPTIONS_SAMPLER_SAMPLINGSERVERURL TYK_GW_TRACER_OPTIONS_SAMPLER_MAXOPERATIONS TYK_GW_TRACER_OPTIONS_SAMPLER_SAMPLINGREFRESHINTERVAL TYK_GW_TRACER_OPTIONS_REPORTER_QUEUESIZE TYK_GW_TRACER_OPTIONS_REPORTER_BUFFERFLUSHINTERVAL TYK_GW_TRACER_OPTIONS_REPORTER_LOGSPANS TYK_GW_TRACER_OPTIONS_REPORTER_LOCALAGENTHOSTPORT TYK_GW_TRACER_OPTIONS_REPORTER_COLLECTORENDPOINT TYK_GW_TRACER_OPTIONS_REPORTER_USER TYK_GW_TRACER_OPTIONS_REPORTER_PASSWORD TYK_GW_TRACER_OPTIONS_HEADERS_JAEGERDEBUGHEADER TYK_GW_TRACER_OPTIONS_HEADERS_JAEGERBAGGAGEHEADER TYK_GW_TRACER_OPTIONS_HEADERS_TRACECONTEXTHEADERNAME TYK_GW_TRACER_OPTIONS_HEADERS_TRACEBAGGAGEHEADERPREFIX TYK_GW_TRACER_OPTIONS_BAGGAGERESTRICTIONS_DENYBAGGAGEONINITIALIZATIONFAILURE TYK_GW_TRACER_OPTIONS_BAGGAGERESTRICTIONS_HOSTPORT TYK_GW_TRACER_OPTIONS_BAGGAGERESTRICTIONS_REFRESHINTERVAL TYK_GW_TRACER_OPTIONS_THROTTLER_HOSTPORT TYK_GW_TRACER_OPTIONS_THROTTLER_REFRESHINTERVAL TYK_GW_TRACER_OPTIONS_THROTTLER_SYNCHRONOUSINITIALIZATION