Add a smart date predicate

[rgehan]

For now, we cannot search issues/PR by their creation date. Ideally, I'd like to be able to do something like:

• Search for issues/PR that are older than: 1 day, 1 week, 1 month.

I think we could create something smart that would dynamically generate the date corresponding to the "range" we want and use it in a filter condition.

Reference: https://help.github.com/articles/searching-issues-and-pull-requests/#search-by-when-an-issue-or-pull-request-was-created-or-last-updated

[aveselovalova]

Hi! I'd like to do this issue

[rgehan]

@honeyyenoh You go ahead, tell me if you have any question about how the extension works :)