fix: hide "Create Workspace" button for deleted templates (#22092)

**Background**

Reported in #17417, there is a `deleted` query parameter supported by
/api/v2/templates, but we do not respect this field on the client,
showing the "Create Workspace" button for deleted templates.

**Expected Behavior**

Don't show the "Create Workspace" button for deleted templates.

**Notes**

This PR adds a new `deleted` field to the templates API response.

Co-authored-by: Danielle Maywood <danielle@themaywoods.com>

coderd/apidoc/docs.go

@@ -18919,6 +18919,9 @@ const docTemplate = `{
                 "default_ttl_ms": {
                     "type": "integer"
                 },
+                "deleted": {
+                    "type": "boolean"
+                },
                 "deprecated": {
                     "type": "boolean"
                 },

coderd/apidoc/swagger.json

@@ -17306,6 +17306,9 @@
 				"default_ttl_ms": {
 					"type": "integer"
 				},
+				"deleted": {
+					"type": "boolean"
+				},
 				"deprecated": {
 					"type": "boolean"
 				},

coderd/templates.go

@@ -1131,6 +1131,7 @@ func (api *API) convertTemplate(
 		RequireActiveVersion:    templateAccessControl.RequireActiveVersion,
 		Deprecated:              templateAccessControl.IsDeprecated(),
 		DeprecationMessage:      templateAccessControl.Deprecated,
+		Deleted:                 template.Deleted,
 		MaxPortShareLevel:       maxPortShareLevel,
 		UseClassicParameterFlow: template.UseClassicParameterFlow,
 		CORSBehavior:            codersdk.CORSBehavior(template.CorsBehavior),

coderd/templates_test.go

@@ -1801,6 +1801,49 @@ func TestDeleteTemplate(t *testing.T) {
 		require.ErrorAs(t, err, &apiErr)
 		require.Equal(t, http.StatusForbidden, apiErr.StatusCode())
 	})
+
+	t.Run("DeletedIsSet", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, &coderdtest.Options{IncludeProvisionerDaemon: true})
+		user := coderdtest.CreateFirstUser(t, client)
+		version := coderdtest.CreateTemplateVersion(t, client, user.OrganizationID, nil)
+		template := coderdtest.CreateTemplate(t, client, user.OrganizationID, version.ID)
+		coderdtest.AwaitTemplateVersionJobCompleted(t, client, version.ID)
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		// Verify the deleted field is exposed in the SDK and set to false for active templates
+		got, err := client.Template(ctx, template.ID)
+		require.NoError(t, err)
+		require.False(t, got.Deleted)
+	})
+
+	t.Run("DeletedIsTrue", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, &coderdtest.Options{IncludeProvisionerDaemon: true})
+		user := coderdtest.CreateFirstUser(t, client)
+		version := coderdtest.CreateTemplateVersion(t, client, user.OrganizationID, nil)
+		template := coderdtest.CreateTemplate(t, client, user.OrganizationID, version.ID)
+
+		coderdtest.AwaitTemplateVersionJobCompleted(t, client, version.ID)
+
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		err := client.DeleteTemplate(ctx, template.ID)
+		require.NoError(t, err)
+
+		// Verify the deleted field is set to true by listing templates with
+		// deleted:true filter.
+		templates, err := client.Templates(ctx, codersdk.TemplateFilter{
+			OrganizationID: user.OrganizationID,
+			SearchQuery:    "deleted:true",
+		})
+		require.NoError(t, err)
+
+		require.Len(t, templates, 1)
+		require.Equal(t, template.ID, templates[0].ID)
+		require.True(t, templates[0].Deleted)
+	})
 }
 
 func TestTemplateMetrics(t *testing.T) {