fix: resolve serialization errors in .NET examples

[moonshxne]

This ended up being a slightly bigger commit than I anticipated. But, I essentially did two things:

• Annotate all *Result types in Mondocks.Net/Types.fs with [<BsonIgnoreExtraElements>]; otherwise, the .NET MongoDB Driver freaks out that the schema doesn't match exactly.

• Avoid serializing each Index object in the IndexBuilder. When I first ran the example in samples/Indexes, it failed with this exception:

Unhandled exception. MongoDB.Driver.MongoCommandException: Command createIndexes failed: BSON field 'createIndexes.indexes.0' is the wrong type 'string', expected type 'object'.

So we DON'T need the serialization step in the IndexBuilder anymore (though I kept the interface the same).

Finally, I added a Nix flake with a very simple devShell because that's just what I'm used to developing with 😅.

[moonshxne]

Fixes #36.

[AngelMunoz]

Over all looks great!

I'm not entirely sure about the nix flake though if you don't mind me pinging you if something weird arises with that it's fine to keep

I'll try to give it a go this week and see how it goes!

[moonshxne]

Feel free to ignore/delete the Nix flake if you're not interested 😅. I'm not building anything, just providing a very simple devShell that brings dotnet6.0 into the $PATH. (But, if you have any questions, feel free to ping me!)