Data source plugin: Improve error message when plugin has connection issues (#102625)

* Improve data source error message when stackID

* Update comment

* Revert "Update comment"

This reverts commit 48922bc552.

* Revert "Improve data source error message when stackID"

This reverts commit 4bf0a2f7b7.

* Make public messagic configurable based on context

* Update, simplify

* Update

* Update getting stack

* Update pkg/plugins/errors.go

Co-authored-by: Andres Martinez Gotor <andres.martinez@grafana.com>

* Refactor test to test for when context has stack value

* Remove duplicated test

* Fix error checking logic

---------

Co-authored-by: Andres Martinez Gotor <andres.martinez@grafana.com>

pkg/plugins/manager/client/client.go

@@ -35,7 +35,6 @@ var passthroughErrors = []error{
 	plugins.ErrPluginUnavailable,
 	plugins.ErrMethodNotImplemented,
 	plugins.ErrPluginGrpcResourceExhaustedBase,
-	plugins.ErrPluginGrpcConnectionUnavailableBase,
 }
 
 type Service struct {
@@ -66,6 +65,12 @@ func (s *Service) QueryData(ctx context.Context, req *backend.QueryDataRequest)
 			}
 		}
 
+		// If the error is a plugin grpc connection unavailable error, return it directly
+		// This error is created dynamically based on the context, so we need to check for it here
+		if errors.Is(err, plugins.ErrPluginGrpcConnectionUnavailableBaseFn(ctx)) {
+			return nil, err
+		}
+
 		if errors.Is(err, context.Canceled) {
 			return nil, plugins.ErrPluginRequestCanceledErrorBase.Errorf("client: query data request canceled: %w", err)
 		}