Opening this issue to track supporting .NET 7.

Assumed release date is Nov 11, listed on dotnet's milestone: https://github.com/dotnet/runtime/milestone/82

Tracking Previews

• Preview 3 was released on April 13th: https://devblogs.microsoft.com/dotnet/announcing-dotnet-7-preview-3/
• Preview 6 was released on July 12th: https://devblogs.microsoft.com/dotnet/announcing-dotnet-7-preview-6/
• Preview 7 was released on August 9th: https://devblogs.microsoft.com/dotnet/announcing-dotnet-7-preview-7/
• Release Candidate 1 was released on September 14th: https://devblogs.microsoft.com/dotnet/asp-net-core-updates-in-dotnet-7-rc-1/
• Release Candidate 2 was released on October 11th: https://devblogs.microsoft.com/dotnet/announcing-dotnet-7-rc-2/
• GA Nov 8th: https://devblogs.microsoft.com/dotnet/announcing-dotnet-7/

TODO

• Update builds, add support for latest .NET 7 Preview
• Update test matrix, add .NET 7
• remove "preview" from builds after .NET 7 official release (Nov)