Add otel instrumentation to gocache and modproxy components

[grambbledook]

This pr adds a basic otel instrumentation to go-cache-plugin

# Setup env variable for tracing
export GOCACHE_ENABLE_TRACING=true  
export GOCACHE_TRACING_OTEL_COLLECTOR="localhost:4319" 

# Or Use RUN_xxx env variables to  compute trace and parent span ids
export TRACING_TRACE_ID="cfe93a0cde6f53f539e0eaff28e05ef4" 
export TRACING_PARENT_SPAN_ID="7e173813d01cc668" 

# setup local cache 
export GOCACHE_LOCAL_ONLY=true
export GOCACHE_DIR=/tmp/gocache
export GOCACHE_MODPROXY_NOCACHE=true

# start go cache process
go-cache-plugin serve --plugin 5930 --http=localhost:5970 --modproxy \
--local-cache --cache-dir=/tmp/gocache

# Set up go mod proxy and gocacheprog tool to intercept requests and report traces
export GOPROXY=http://localhost:5970/mod  
export GOCACHEPROG="./go-cache-plugin connect 5930" 

# Execute grafana build
make build-go