.NET: Use observability term (#889)

* use observability term instead of telemetry

* rename telemetry folder to observability

* rolledback changed sample description

dotnet/agent-framework-dotnet.slnx

@@ -46,7 +46,7 @@
     <Project Path="samples/GettingStarted/Agents/Agent_Step05_StructuredOutput/Agent_Step05_StructuredOutput.csproj" />
     <Project Path="samples/GettingStarted/Agents/Agent_Step06_PersistedConversations/Agent_Step06_PersistedConversations.csproj" />
     <Project Path="samples/GettingStarted/Agents/Agent_Step07_3rdPartyThreadStorage/Agent_Step07_3rdPartyThreadStorage.csproj" />
-    <Project Path="samples/GettingStarted/Agents/Agent_Step08_Telemetry/Agent_Step08_Telemetry.csproj" />
+    <Project Path="samples/GettingStarted/Agents/Agent_Step08_Observability/Agent_Step08_Observability.csproj" />
     <Project Path="samples/GettingStarted/Agents/Agent_Step09_DependencyInjection/Agent_Step09_DependencyInjection.csproj" />
     <Project Path="samples/GettingStarted/Agents/Agent_Step10_AsMcpTool/Agent_Step10_AsMcpTool.csproj" />
     <Project Path="samples/GettingStarted/Agents/Agent_Step11_UsingImages/Agent_Step11_UsingImages.csproj" />
@@ -61,7 +61,7 @@
     <Project Path="samples/GettingStarted/ModelContextProtocol/Agent_MCP_Server/Agent_MCP_Server.csproj" />
     <Project Path="samples/GettingStarted/ModelContextProtocol/Agent_MCP_Server_Auth/Agent_MCP_Server_Auth.csproj" />
   </Folder>
-  <Folder Name="/Samples/GettingStarted/Telemetry/">
+  <Folder Name="/Samples/GettingStarted/Observability/">
     <Project Path="samples/GettingStarted/AgentOpenTelemetry/AgentOpenTelemetry.csproj" />
   </Folder>
   <Folder Name="/Samples/GettingStarted/Workflows/">