Migrate Sample: Build web APIs with OData support using ASP.NET Core #69

Please review Sample: Build web APIs with OData support using ASP.NET Core and let me know if you'd like me to migrate that tutorial to this repo.

Outline of proposed work

• Create AspnetCore folder in OData-docs/Odata-docs/webapi/
• Move the sample/tutorial to the AspnetCore folder.
• Add ASP.NET Core 3.0 version.
• Add tutorial to the TOC

Does your repo support importing snippets? If not, would you like me to enable that?
Does your repo support versions? If not, would you like me to enable that.

::: moniker range=">= aspnetcore-3.0"
//  3.0 version here
::: moniker-end

::: moniker range="< aspnetcore-3.0"
// 2.2 version here
::: moniker-end