How to use `$addFields` aggregation

[lenguyenthanh]

First of all, thanks for your work on this library, We started to use it in lichess.org and it's just wonderful to use.

I just wonder how to use $addFields aggregation with mongo4cats. I see that We support some similar operation like unwind, replaceWith but not addFields.

I can create Document, Bson by my own, but I couldn't find a way to create an Aggregate our of them.

So, imho, We could solve this by two ways:

• support $addFields and some other missing aggregations out of the box
• support a way to construct aggration from org.boson.Bson or BsonValue.

I'm willing to create a PR if you think it's a good idea?

[Kirill5k]

@lenguyenthanh, I've just did a release with your change in it. You should now be able to use it in your code (v0.7.7) 👍

[lenguyenthanh]

thanks a lot @Kirill5k for your quick help ❤️, really appreciated.

We still some other missing aggregation operators. I'll continue work on those. Do prefer one pr per operator or one pr with all operators (with careful one commit per operator)?

[Kirill5k]

Either way is fine, whichever is easier for you.

If you give me names of these operator, I could help you out on this as well.

[lenguyenthanh]

I created a new issue with all the missing aggregation operators: #43