Objective

To check whether developers set proper handler name in repo or not before executing sls deploy

What experience is expected?

When developers execute ptmpdy check, these behaviors are expected at least.

1. If declared handlers in serverless.yml does not exist in repo, cli exit as 1
2. Otherwise, cli exit as 0

TBD: Spec

@app.command() 
def check(
    fp: Optional[str] = Option(default=None, help="if None, cli loads from current directory"), 
) -> None: 
    ...