Build metadata endpoint and directory walker

Summary

We are supporting metadata upload to k-v store for key-value pair key->conf right now. We want to add a general class metadata endpoint to support more potential use cases.

This PR is to add two general class MetadataEndPoint and MetadataDirWalker

MetadataEndPoint:

case class MetadataEndPoint[Conf <: TBase[_, _]: Manifest: ClassTag](
    extractFn: (String, Conf) => (String, String),
    name: String
)

Defined with a extract function and an end point name. Extract function extracts the key-value pair from Conf(could be Join/GroupBy/StagingQuery) and file path(string). The name is the dataset name when we send the data to k-v store.

MetadataDirWalker:

class MetadataDirWalker(dirPath: String, metadataEndPointNames: List[String])

Go through the directory to iterate over all the config files and generate k-v pair metadata based on the metadata end points provided.

The PR adds two metadata endpoint ZIPLINE_METADATA and ZIPLINE_METADATA_BY_TEAM

CHRONON_METADATA: key -> conf json in string format e.g : joins/team/team.example_join.v1 -> {...}

CHRONON_METADATA_BY_TEAM: type/team -> list of key in string format e.g : joins/team -> a, b, c

Why / Goal

Test Plan

[ ] Added Unit Tests
[ ] Covered by existing CI
[x] Integration tested

Testing by running the metadata-upload and fetch command for a join. https://docs.google.com/document/d/1X7n_jskS7JyiiqVB3pStgPilg6luy23ho58twCHeip8/edit?usp=sharing

Checklist

[ ] Documentation update

airbnb / chronon