Model API endpoints v2.0

[alexmavr]

The existing API structure reflects the top-down hierarchy of the actual model. However, there might be use cases where extracting bulk metrics and/or stats might be useful.

Examples:
/metrics/namespaces/{namespace-name}/pods/?label=X&value=Y&start=Z&end=K
returns all metrics of all pods in a namespace that satisfy the specified label:value pair within the optional start and end intervals.

/stats/namespaces/{namespace-name}/pods/{pod-name}/containers?label=X&value=Y&start=Z&end=K
returns all stats of all containers in a pod that satisfy the specified label:value pair within the optional start and end intervals.

Similar top-level endpoints can be implemented, such as /metric-sum/, depending on actual usecases of the model.

\cc @vishh @mwielgus

[vishh]

@piosz: This is a proposal for a more long term API. Kindly take a look.

[piosz]

cc @fgrzadkowski

[fgrzadkowski]

This will be substituted by metrics API.