add condition to get commits within 30 days of the latest commit

[s7tya]

closes #1920

I'm not sure if this is a good implementation.

[Kobzol]

This is a bit hacky, yeah 😅 And it won't work for locally benchmarked commits, since these are not master commits.

Ideally, we should move the hardcoded condition that None as a left bound means "now() - 30 days" from within the Bound implementation itself, and just treat bound=none, left to be the first commit, and bound=none, right to be the last commit. But I'm a bit wary of doing that, because the bounds are used in a bunch of places, and doing this change might break a lot of stuff.

I realize now that it's quite difficult to make this work both locally and on the live server, because there we have very different requirements. On perf.RLO, we want to show only master commits, with a default range of [-30 days, now()]. Locally, we want to show all commits, with a default range of [first commit, last commit] (or [-30 days, last commit]). While the [-30 days, last commit] bound could work both for local and perf.RLO usage, the is_master() condition is a problem.

I'm not really sure what to do with that. We could display also try/local commits e.g. in debug mode, but that's quite unintuitive. We could add some parameter to the website, or check if the URL e.g. starts with localhost, but even then I wouldn't want to check this condition in Bound::[left/right]_match, but rather in comparison.rs. But for that we'd probably need to refactor the bounds quite a lot, add information to them if they should keep only master commits etc.

Maybe we could modify collector so that it puts local commits into the DB as master commits, and fills out the date for them 🤔 That could help unifying the local and production environments.