[#3948] Update dotnet samples to target .Net 8 - Skills samples

[sw-joelmut]

Addresses #3948

minor

[!IMPORTANT] These changes depend on PR https://github.com/microsoft/BotBuilder-Samples/pull/3982 being merged, so the CI pipeline pass successfully with .NET 8.

Description

This PR updates the Skills samples to target .NET 8

Specific Changes

• Updated the following samples to target .NET 8
  • 80.skills-simple-bot-to-bot
  • 81.skills-skilldialog
  • 82.skills-sso-cloudadapter
• README files updated to target .NET 8
• Fixed an issue with skills-sso-cloudadapter when obtaining the Skill ID from claims.

Testing

These images show the updated bots working as expected. 80.skills-simple-bot-to-bot 81.skills-skilldialog 82.skills-sso-cloudadapter