Implement milestone payload and query builder

[gsmet]

Description

Implement the payload for milestone... Don't know how I missed it earlier as it's quite useful.
Also allow to query the milestones with more options as it's useful to be able to sort them properly.

While a query builder is a bit heavy for what we actually need to do here, I favored a pattern we are using globally, and we never know what they might add to the API later.

I wanted to be able to sort the milestones.
Even that is extremely limited...
Believe it or not, we can't sort by close dates.

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[gsmet]

hey @bitwiseman , long time no see :). I hope you're doing well.

[gsmet]

BTW, I should explain a bit why this is critical for us: I need to get the 20 latest milestones and currently we can't do it. Meaning that I'm forced to get the ~500 milestones we have in the Quarkus project and then filter them. And the GitHub API rate limiting is not exactly happy about it :).