Add two troubleshooters

docs/troubleshooting/connection-string-missing.md

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+---
+title: The connection string is missing
+description: Learn how to troubleshoot the error "ConnectionString is missing" during execution of your app.
+ms.date: 07/03/2024
+---
+
+# The specified name is already in use
+
+## Symptoms
+
+When your app accesses a service that needs one of the components in your app, it may fail with an exception similar to the following:
+
+> "InvalidOperationException: ConnectionString is missing."
+
+## Possible solutions
+
+Verify that the name of the resource, for instance a database resource, is the same in the AppHost and the Service that fails. 
+
+For example, if the AppHost defines a PostgreSQL resource with the name db1 like this: 
+
+```csharp
+var db1 = builder.AddPostgres("pg1").AddDatabase("db1"); 
+```
+
+Then the service needs to resolve the resource with the same name `db1`. 
+
+```csharp
+var builder = WebApplication.CreateBuilder(args); 
+
+builder.AddNpgsqlDbContext<MyDb1Context>("db1"); 
+```
+
+Any other value than the one provided in the AppHost will result in the exception message described above.

docs/troubleshooting/container-runtime-unhealthy.md

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+---
+title: Container runtime appears to be unhealthy
+description: Learn how to troubleshoot the error "Container runtime 'docker' was found but appears to be unhealthy" during execution of your app.
+ms.date: 07/03/2024
+---
+
+# Container runtime appears to be unhealthy
+
+## Symptoms
+
+When starting the AppHost the dashboard doesn't show up and an exception stack trace similar to this example is displayed in the console: 
+
+```sh
+info: Aspire.Hosting.DistributedApplication[0] 
+      Aspire version: 8.1.0-dev 
+info: Aspire.Hosting.DistributedApplication[0] 
+      Distributed application starting. 
+info: Aspire.Hosting.DistributedApplication[0] 
+      Application host directory is: D:\aspire\playground\PostgresEndToEnd\PostgresEndToEnd.AppHost 
+fail: Microsoft.Extensions.Hosting.Internal.Host[11] 
+      Hosting failed to start 
+      Aspire.Hosting.DistributedApplicationException: Container runtime 'docker' was found but appears to be unhealthy. The error from the container runtime check was error during connect: this error may indicate that the docker daemon is not running: Get "http://%2F%2F.%2Fpipe%2Fdocker_engine/v1.45/containers/json?limit=1": open //./pipe/docker_engine: The system cannot find the file specified.. 
+```
+
+## Possible solutions
+
+Confirm that Docker is installed and running. 
+
+* On Windows, check that in the system tray the Docker icon is present and marked as "Running". 
+
+* On Linux, check that "docker ps -a" returns success.