conditional instrumentation and profiling options for server example

v3/examples/server/README.md

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+By default, building the server application here (e.g., via `go build` or `go run main.go`) will create a simple web service that is instrumented by the Go Agent. This
+has a number of HTTP endpoints which demonstrate different capabilities:
+   `/`
+   `/add_attribute`
+   `/add_span_attribute`
+   `/async`
+   `/background_log`
+   `/background`
+   `/browser`
+   `/custom_event`
+   `/custommetric`
+   `/external`
+   `/ignore`
+   `/log`
+   `/message`
+   `/mysql`
+   `/notice_error_with_attributes`
+   `/notice_error`
+   `/notice_expected_error`
+   `/roundtripper`
+   `/segments`
+   `/set_name`
+   `/version`
+All of these are served from TCP port 8000 on the local host.
+
+However, if you build the application with `go build -tags control`, you'll get a "control" version which does not use the Go Agent, to compare against if you are testing to see how an app performs with and without the agent.
+
+If you build with `go build -tags profiling`, you will get a version which generates CPU and memory profiling data. You can get both (a profiling, non-agent version) by including both tags as `go build -tags profiling,control`.

v3/examples/server/instrumentation.go

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+//go:build !control
+// +build !control
+
+package main
+
+const instrumentCode = true