Expand benchmark tooling to include memory usage

[ivanvc]

What would you like to be added?

The current benchmarking (from tools/rw-heatmaps, tools/benchmark) only measures the r/w operations (QPS). The release v3.6 minor has memory improvements, reducing the memory footprint. However, there's no current tooling to benchmark and report these results.

Why is this needed?

To provide comparisons of the memory usage footprint across different versions.

[ivanvc]

@serathius, @ahrtr mentioned that you can share some ideas on how we can achieve this. Would you be able to do so? Thanks :)