backend benchmarking main ticket

parent ticket for all benchmarking tasks:

• Make room for performance tests somewhere in src/ and write a separate Ant task to run them. (#15753 (moved))
• Take an out/summary file as input and generate good sample requests for a RequestHandler performance test class. Also write that test class.
• Write a performance test class for ResponseBuilder, probably requiring a successful run of the hourly updater to populate the out/ directory.
• Write another performance test class for DocumentStore that takes a populated status/ and out/ directory as input and performs a random series of listing, retrieving, removing, and storing documents. Ideally, the test class would make sure that the contents in both directories are still the same after running the test.