feat: 📦 Provide RudderStack Chart with HPA

Description of the change

This PR aims to provide the RudderStack helm as a Chart while providing the following features:

Feature: Provide Chart structure.
Feature: Release Chart on master merge.
Feature: Move (on demand) Postgres resources to a sidecar approach.
Feature: Enable HPA for the Transformations Deployment resource.
Feature: Enable HPA for the Backend Statefulset resource.
Feature: PreStop Hook to prevent data loss on new deployments or autoscaling down processes.
Fix: backend.uploadFreqInS typo.
Feature: Add env tag to Telegraf global tags.
Feature: Allow to define extraEnvVars in the Telegraf pod.

⚠️ Note: It requires the RudderStack team to enable gh-pages to host the Chart.

PR #43

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