Support executables with both Gin and net/http

[mariomac]

The way the instrumenter currently works, it searches either for net/http.HandlerFunc.ServeHTTP or github.com/gin-gonic/gin.(*Engine).ServeHTTP, and then adds an instrumentation point to the latest found function, but not to both.

This could lead to not being able to instrument customers that are progresssively migrating away from Gin to another framework.

[mariomac]

Closing as it is not true. Current integration tests executable has both gin, gorilla and net/http