fix: mark presets as validation_failed to prevent endless prebuild retries (#22085)

## Description

- Updates `wsbuilder` to return a `BuildError` with
`http.StatusBadRequest` to signify a "validation error" on missing or
invalid parameters
- Adds a short-circuit in `prebuilds.StoreReconciler` to mark presets
for which creating a build returns a "validation error" as "validation
failed" and skip further attempts to reconcile.
- Adds a test to verify the above
- Introduces a new Prometheus metric
`coderd_prebuilt_workspaces_preset_validation_failed` to track the above

Closes: https://github.com/coder/coder/issues/21237

---------

Co-authored-by: Cian Johnston <cian@coder.com>

coderd/wsbuilder/builderror_test.go

@@ -0,0 +1,64 @@
+package wsbuilder_test
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/hashicorp/hcl/v2"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/xerrors"
+
+	"github.com/coder/coder/v2/coderd/dynamicparameters"
+	"github.com/coder/coder/v2/coderd/wsbuilder"
+)
+
+func TestBuildErrorResponseDelegation(t *testing.T) {
+	t.Parallel()
+
+	t.Run("plain_error", func(t *testing.T) {
+		t.Parallel()
+
+		be := wsbuilder.BuildError{
+			Status:  http.StatusBadRequest,
+			Message: "bad",
+			Wrapped: xerrors.New("oops"),
+		}
+
+		status, resp := be.Response()
+		require.Equal(t, http.StatusBadRequest, status)
+		require.Equal(t, "bad", resp.Message)
+		require.Contains(t, resp.Detail, "oops")
+		require.Empty(t, resp.Validations)
+	})
+
+	t.Run("responder_error", func(t *testing.T) {
+		t.Parallel()
+
+		inner := &dynamicparameters.DiagnosticError{
+			Message: "resolve parameters",
+			KeyedDiagnostics: map[string]hcl.Diagnostics{
+				"param1": {
+					{
+						Severity: hcl.DiagError,
+						Summary:  "required parameter",
+					},
+				},
+			},
+		}
+
+		be := wsbuilder.BuildError{
+			Status:  http.StatusBadRequest,
+			Message: "build error wrapper",
+			Wrapped: inner,
+		}
+
+		status, resp := be.Response()
+
+		// Should delegate to the inner DiagnosticError's response.
+		innerStatus, innerResp := inner.Response()
+		require.Equal(t, innerStatus, status)
+		require.Equal(t, innerResp.Message, resp.Message)
+		require.Len(t, resp.Validations, 1)
+		require.Equal(t, "param1", resp.Validations[0].Field)
+	})
+}