[Python] Add feast feature store handler for enrichment transform

[riteshghorse]

Implement Feast feature store handler for enrichment transform. To setup the feast repository for GCP, see this notebook.

Example usage:

handler = FeastFeatureStoreEnrichmentHandler(
        entity_id='user_id',
        feature_store_yaml_path=<GCS_PATH>,
        feature_service_name=<service_name_used_while_deployment>,
)

with beam.Pipeline() as p:
  output = (
                  p
                  ....
                  | "Enrich with Feast" >> Enrichment(handler)
                  ....
  )

Fixes #30964

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[riteshghorse]

Feast integration tests passed

Unrelated failures in other test suites

[riteshghorse]

assign set of reviewers

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[riteshghorse]

Friendly ping!

[riteshghorse]

R: @damccorm

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[damccorm]

Overall looks pretty good, had a few comments

[riteshghorse]

Feast tests passing-

[damccorm]

Nice! Just had one last small comment about the pydoc, otherwise LGTM

[damccorm]

LGTM once checks pass - thanks!

[riteshghorse]

Unrelated failures in postcommit with pytorch and tensorflow. Merging this one!
Thanks for the review!