[Feature Request]: Enrichment Transform

[riteshghorse]

What would you like to happen?

Implement a enrichment transform to enrich a PCollection by making a request to the external source.

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

Issue Components

• [X] Component: Python SDK
• [ ] Component: Java SDK
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[riteshghorse]

Tasks to mark this complete

• [x] Core Enrichment transform
• [x] BigTable handler for enrichment transform
• [x] HTTP test with Mock API

[riteshghorse]

Design doc - https://s.apache.org/enrichment-transform