Add MongoDB load generation support

[mariaalons]

Adds a load generator to the MongoDB sample app so the dashboard panels have live data. Seeds a user collection and runs a continuous CRUD workload in both the sharded and single-replicaset.

[Dasomeone]

I forgot to mentioned on the earlier review of the linked mixin, but one thing you can do with this PR is also adjust the pass rate requirement. Currently it's anything >45% but could/should likely be raised up near the 80% rule of thumb if the operations and qps metrics get sorted

[mariaalons]

I forgot to mentioned on the earlier review of the linked mixin, but one thing you can do with this PR is also adjust the pass rate requirement. Currently it's anything >45% but could/should likely be raised up near the 80% rule of thumb if the operations and qps metrics get sorted

Thank you for pointing it out! I managed to update this to the 60%

[Dasomeone]

Fantastic work, thank you very much! Now populates all the panels and dashboards of the updated mixin :)