Built-in Rate Limiting support - part of .NET 7

[cristipufu]

If you haven't heard yet, .NET 7 comes with built-in support for Rate Limiting (in-memory): https://devblogs.microsoft.com/dotnet/announcing-rate-limiting-for-dotnet/

I have created another repository for multi-node deployments (with Redis) and my future contributions will be focused on this new library: https://github.com/cristipufu/aspnetcore-redis-rate-limiting