[Core feature] [Flytekit] Add Agent Template in Pyflyte Init

[mao3267]

Motivation: Why do you think this is important?

Some concepts are not clearly documented when creating custom agents, resulting in misunderstandings and hardship for users. Therefore, we want to provide a template in Pyflyte init to help users with this.

Goal: What should the final outcome look like, ideally?

Users can create a project with the custom agent template by pyflyte init --template basic-custom-agent PROJECT_NAME

Describe alternatives you've considered

Only provide the links to example repositories in the documentation.

Propose: Link/Inline OR Additional context

Template draft: https://github.com/Future-Outlier/flyte-custom-agent-template

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes