Add rate limit to requests sent to other services

[cuixq]

OSV-Scanner sends requests to other services for various purposes. Considering there may be rate limit policies for these services, we should add rate limit to these requests. golang.org/x/time/rate might be something useful here.

[sureshkrishnan-v]

Hello! I would like to contribute to this issue. Could you please assign it to me? Thank you! and i am new to open source and i have 1 year experience as a golang developer can you guys please guide me to solve this issue

[cuixq]

@sureshkrishnan-v I think this may not be a good first issue since it requires familiarity on this repository, feel free to contribute to other good first issues!