Proxy recorder should create the sample before executing it

**Sebb** ([Bug 55532](https://bz.apache.org/bugzilla//show_bug.cgi?id=55532&redirect=false)):
The Proxy Sampler currently adds the generated sample to the test plan after executing it.

This is because content-type filtering depends on the response.

In case of sample failure, it might be better to add the sample to the test tree anyway, and then delete it later?

Or, if content filtering is not being used, at least then the sample could be added earlier.

Needs investigation to see how feasible this is.

OS: All