Add regression test to detect service broken and performance degradation

[FanhaiLu1]

We saw few service broken and performance degradation in last two weeks, it's hard to identify which PR cause the issues when the issue was found few days later.

Right now, there is no regression test for jetstream pytorch serving. Regression test is necessary to catch the broken or degradation bug.

[FanhaiLu1]

@qihqi @wang2yn84 Let's revisit this issue now. Having regression test is critical to catch the performance degradation. @sixiang-google Since the infra is ready, could you work on regression test for ML perf offline and oneline?

[wang2yn84]

+1. Top priority now.