Add Instructions for Namespace Template in Development Environment Setup Guide

[Yicheng-Lu-llll]

Describe your changes

Added instructions for adding the namespace template for the cluster resource controller in the Development Environment Setup Guide .

With namespace template, the cluster resource controller will automatically create namespaces for existing projects.
For example, with Flyte's default project "flytesnacks", the controller will auto-create the following namespaces: flytesnacks-staging, flytesnacks-development, and flytesnacks-production.

Previously, in the Development Environment Setup Guide, namespaces were created manually, which was suboptimal.

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Screenshots

Note to reviewers