Docs: Actor serialization documentation

[WhitWaldo]

Description

This is my first draft of a new page in the documentation detailing how serialization works using the Dapr .NET Actors SDK today. It's my response to the issue raised https://github.com/dapr/dotnet-sdk/issues/679 which is marked as a bug, but reflects a misunderstanding of how the serialization engine handles records. My goal with adding this page is to provide an upfront resource for developers using actors to understand why serialization may not be working as expected out of the box and provide not only a solution, but an explanation.

I detail how serialization is performed to illustrate the benefits to either going the parameterless constructor route or decorating types and members with the applicable attributes and then share my recommendation to use attributes and why. I dive through several examples documenting expectations in classes, structs and records and then speak a bit to other related scenarios (collections, enums, polymorphic types) towards the end pointing back to the official documentation to keep this document from getting too verbose.

This is a documentation update only and changes no code in the SDK.

This replaces a previous PR in which I had a commit that had an invalid DCO.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #679

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

~ [ ] Code compiles correctly~ ~ [ ] Created/updated tests~

• [X] Extended the documentation

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[onionhammer]

This doesn't mention JSON serialization, which IIRC is an option now?

[WhitWaldo]

@onionhammer That's right. This was intended largely to speak to the issue raised in #679 to explain why data contract serialization and records regarding actors didn't appear to work automagically (and to speak to why the new primary class constructors might yield a similar experience), but I didn't dig into the JSON serialization route at all.