feat(metric_unify): refactor and add diff command

[keroro520]

Resolve #1155

Usage:

metric_unify summary --metrics-json <METRICS_JSON>

metric_unify aggregate --metrics-json <METRICS_JSON> --aggregation-json <AGGREGATION_JSON>

metric_unify diff --metrics-json <METRICS_JSON> --prev-metrics-json <PREV_METRICS_JSON>

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The "main" branch has significant changes, need to resolve conflicts.

[jonathanpwang]

The way I have it set up now, diff is auto detected if the optional arg --prev-json-paths is provided

[jonathanpwang]

@keroro520 just checking if you needed any help here (no rush)

[keroro520]

@keroro520 just checking if you needed any help here (no rush)

Thank you for your kind reminder @jonathanpwang
I've been struggling with other tasks lately and will take some time to resolve the conflicts asap.