Add Serilog logging and hosting

[KuraiAndras]

The NuGet package needs to respect a few constraints in order to be listed in the curated list:

• Add a link to the NuGet package:
• https://www.nuget.org/packages/Serilog.Extensions.Hosting/4.2.0
• It must have non-preview versions (e.g 1.0.0 but not 1.0.0-preview.1)
• It must provide .NETStandard2.0 assemblies as part of its package
• The lowest version added must be the lowest .NETStandard2.0 version available
• The package has been tested with the Unity editor
• The package has been tested with a Unity standalone player
  • if the package is not compatible with standalone player, please add a comment to a Known issues section to the top level readme.md
• All package dependencies with .NETStandard 2.0 target must be added to the PR (respecting the same rules above)
  • Note that if a future version of the package adds a new dependency, this dependency will have to be added manually as well

[KuraiAndras]

So I have looked at the PR from #28 . It seems that Serilog.Extensions.Logging should work when serilog/serilog-extensions-logging#192 is done, and then Serilog.Extensions.Hosting should work when they bump their dependency on Serilog.Extensions.Logging. I'll subscribe to their notifications, and when these are done I will update this PR

[nblumhardt]

Should be good to go now 👍

[bdovaz]

We need to create a PR to bump the hosting NuGet package version and depend on logging 3.1.0 to fully unblock this PR

[KuraiAndras]

@bdovaz I have created #69 so that the logging extension can be used before the hosting package is done

[KuraiAndras]

Once serilog/serilog-extensions-hosting#55 is done, I can update the version of the Hosting package

[KuraiAndras]

@xoofx @bdovaz In the meantime .NET 6 came, and I think Microsoft.Extensions.Hosting 6.0.0 relies on Microsoft.Extensions.Features which is a new package. I also added that, since the build was failing