Define and support template development process

[weikanglim]

• Define local development process.
• Define local testing process.
• Define PR validation + automated test process. See Define checklist for new templates to be checked in azure-dev repo #676 for requirements
• Define the strategy for creating a new azd template repo in Azure-Samples #661
• Guidance for sequencing azd dependencies and validation. Needs to be caught during PR validation when surfacing to azd template list.

[vhvb1989]

Some questions I have related to templates:

• Should a template define a version? (I think the current approach is to use git branches for versioning)
• Should it be a template repository schema? A way to tell azd where to discover/pull templates from
• Do we want to have the concept of official templates vs non-official templates ?? As a way to ensure flaky templates ?

[jongio]

Templates are versioned in azure.yaml

[rajeshkamal5050]

Related to #287