Add proper template generation to Feast CLI

[woop]

What this PR does / why we need it:

• Adds proper templating to Feast. Instead of writing repos from inline yaml/code, we now store the templates under sdk/python/feast/templates.
• Templates can be initialized using feast init -t template_name, e.g, feast init -t gcp
• We have templates for local, gcp, and minimal.
• The gcp template is newly added.
• The default template is local. Meaning feast init will use the local template.
• The minimal template can also be selected using feast init --minimal, which creates a nearly empty repository.

Does this PR introduce a user-facing change?:

Templating added to Feast init command

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jklegar, woop

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[jklegar]

/lgtm