Support net6.0,net7.0 and MAUI

[sacOO7]

• Updated netstandard project to include net6.0/net7.0 support.
• Fixed compilation errors due to net6.0/net7.0 inclusion.
• Added tests for net6.0/net7.0.
• Upgraded NetCore3.1 (out of support) test project to Net6 and Net7.
• Updated github workflow for respective platforms.
• Added OS specific agent headers
• Fixed Update release notes with .NET 6 status #1116
• Fixed Dependency .NET 3.1 (LTS) support ends in December 2022 #1153
• Fixed Support for .NET Multi-platform App UI (.NET MAUI) #1178
• Fixed .Net MAUI app throws System.Net.NetworkInformation.NetworkInformationException when creating AblyRealtime object #1205

[sacOO7]

TODO

• Fix tests
• Fix github workflow
• Add agent headers
• Test xamarin project
• Update build script README, check for other README updates

[AndyTWF]

Looks good - there are a few deprecation warnings at the bottom of the Files Changed on the PR (for net6/7), are these quick things we could fix before merging? :)

[sacOO7]

Looks good - there are a few deprecation warnings at the bottom of the Files Changed on the PR (for net6/7), are these quick things we could fix before merging? :)

Yes, I will check if they can be fixed 👍

[owenpearson]

A couple of very minor comments based on just checking that the code looks sensible. I don't know enough about the dotnet platform to be able to comment on the build changes here unfortunately.

[marto83]

Well done. I've got a couple of minor updates, and if you decide maybe remove the enum :) but that's more a preference rather than a hard and fast rule.

[owenpearson]

I don't fully understand the dotnet platform stuff but the code changes LGTM 👍

[marto83]

👍🏼

[sacOO7]

Thanks @marto83 and @owenpearson for the review.

[sacOO7]

Merging the PR since all tests are passing : )