.NET: A2A Agent release

[SergeyMenshykh]

• Review and simplify A2A client samples
  • .NET: Simplify A2A function tool samples #7861
  • .NET: Simplify A2A client-server sample #7891
• Update A2A sample(s) uising MAF A2A agent in A2A repo
• Extend A2A hosting to support tasks: .NET: [Hosting] Track and update A2A Task state after creation #5362
• Review task update functionality
• Review the AgentRunMode functionality: .NET: [BREAKING] Clarify A2A agent run modes #8032
• Upgrade MAF to the latest pre-release A2A nuget
  • Update code to use new API from the PR: refactor: Add metadata parameters to TaskUpdater and MessageResponder methods a2aproject/a2a-dotnet#394
  • Update code to use new API from the PR: fix: remove /card endpoint from HTTP+JSON binding a2aproject/a2a-dotnet#385
• Upgrade MAF to the latest release A2A nuget
• Update documentation
• Blogpost to announce the release