Define common `SampleExecutor` in devtools_testutils

@howieleung did an excellent job writing up a TestClass that allows them to easily wrap their `samples` in recordings without adjustments to the code of the sample itself (beyond the [customizations](https://github.com/Azure/azure-sdk-for-python/blob/de53a2eda95601ff20df68575f7bae67efa8c9b2/sdk/ai/azure-ai-projects/tests/samples/test_samples.py#L301) that enable the playback for the recording).

There is _some_ code here that I'm uncertain will be valid -- namely some of the output processing is rightly tightly bound to AI specifically.

We should A) abstract this code into devtools_testutils B) update the AI SampleExecutor to use this new common class and C) ensure that the common class has customizability to re-enable the newly replaced AI samples.