Propagate Context from entry point to some functions to replace Background/TODO

[sivchari]

Summary

Some function uses context.TODO or context.Background. So it's better to replace these to propagate context cancellation.

Motivation

Currenty, some function uses context.TODO or context.Background. As a result, some connection might be leaked, since the context isn't propagated.
In additional, context.TODO is ambiguous whether these codes are planed to replace right context or not.
Thus, I think it should replace context.Background instead of context.TODO.

Proposal

This migration might be done by 2 step.

1. Add static analysis to forbid context.TODO and context.Background for finding thesd.
2. propagate context from cmd/** to some functions
3. Remain context.Background if it's impossible to replace

What do you think ?