[Typescript] Align snippet generation to specification.

[andrueastman]

Specification for snippets should align to the specification available at https://gist.github.com/sebastienlevert/ae40eb334c3d5a9d4cd3f4a06d2b09be and shared document.

In summary, we should update snippets to

• Have necessary import statements
• Remove client initialization code
• Add comments with links
• Display version of SDK the snippet supports.