It would be nice to have a `json` output option so one could use this to track memory consumption over time via github-action-benchmark

I would like to use this in conjunction with https://github.com/benchmark-action/github-action-benchmark to track the memory performance of my python package over time, as realized through test cases.

Begin by locating how pytest-memray currently emits results and compare that output with github-action-benchmark's expected JSON format. Done means users can request JSON output and consume it in the benchmark workflow to track memory performance from Python test cases.

Written by the indexing model from the issue text.