Snoop: add generated code destination to Benchmark.S

Context

We want to have generated_code_destination in Benchmark to use it in the future for automatic generation of cost_functions in dedicated files and to have an easy way to see what code does the benchmark generate and where.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR