RUMM-610 Add memory consumption benchmarks for data upload

[ncreated]

What and why?

📦 This PR adds benchmarks required to test memory leaks fixed in #180. I'm adding this in a separate PR to master, as on the hotfix branch (starting from 1.2.2), the benchmark target's setup is incomplete.

How?

I added HTTPServerMock instrumentation to the Benchmarks target (to run them against real server).

The test is simple:

measure(metrics: [XCTMemoryMetric()]) {
    (0..<10).forEach { _ in
        let data = Data(repeating: 0x41, count: 10 * 1_024 * 1_024)
        _ = dataUploader.upload(data: data)
    }
}

It measures the memory footprint of uploading 10 data requests, 10MB each.

Running without the fix (we can clearly see over 100MBs of leaked data):

[Memory Physical, kB] 
average: 104956.723, 
relative standard deviation: 0.049%, 
values: [104943.616000, 104910.848000, 104968.192000, 105050.112000, 104910.848000]

Running with #180 hotfix (the memory footprint is negligible):

[Memory Physical, kB] 
average: -2048.819, 
relative standard deviation: -148.466%, 
values: [-7790.592000, -2560.000000, 28.672000, 36.864000, 40.960000],

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference