Add sample project to the repo.

[bruno-garcia]

This helps when developing. A dsn from the sentry-sdks org can be hard coded so pulling the repo and running the samples sends events to a place visible to SDK contributors. Add a README to the sample directory explaining how to run it, and that a DSN needs to be swapped

Examples: https://github.com/getsentry/sentry-dotnet/tree/main/samples/Sentry.Samples.Log4Net

https://github.com/getsentry/sentry-java/tree/main/sentry-samples/sentry-samples-spring-boot