fix(nextjs): if there is no tsconfig.app.json or tsconfig.lib.json then set path to tsconfig.json (#4101)

Storybook configuration could not be added to nextjs apps because they have a tsconfig.json
and
not a tsconfig.app.json

ISSUES CLOSED: #4092

Author: mandarini

packages/storybook/src/schematics/configuration/configuration.ts

@@ -23,6 +23,7 @@ import {
   applyWithSkipExisting,
   isFramework,
   getTsConfigContent,
+  TsConfig,
 } from '../../utils/utils';
 import { CypressConfigureSchema } from '../cypress-project/cypress-project';
 import { StorybookConfigureSchema } from './schema';
@@ -143,21 +144,43 @@ function createProjectStorybookDir(
   };
 }
 
-function getTsConfigPath(tree: Tree, projectName: string): string {
+function getTsConfigPath(
+  tree: Tree,
+  projectName: string,
+  path?: string
+): string {
   const { projectType } = getProjectConfig(tree, projectName);
   const projectPath = getProjectConfig(tree, projectName).root;
   return join(
     projectPath,
-    projectType === 'application' ? 'tsconfig.app.json' : 'tsconfig.lib.json'
+    path && path.length > 0
+      ? path
+      : projectType === 'application'
+      ? 'tsconfig.app.json'
+      : 'tsconfig.lib.json'
   );
 }
 
 function configureTsProjectConfig(schema: StorybookConfigureSchema): Rule {
   const { name: projectName } = schema;
 
   return (tree: Tree) => {
-    const tsConfigPath = getTsConfigPath(tree, projectName);
-    const tsConfigContent = getTsConfigContent(tree, tsConfigPath);
+    let tsConfigPath: string;
+    let tsConfigContent: TsConfig;
+
+    try {
+      tsConfigPath = getTsConfigPath(tree, projectName);
+      tsConfigContent = getTsConfigContent(tree, tsConfigPath);
+    } catch {
+      /**
+       * Custom app configurations
+       * may contain a tsconfig.json
+       * instead of a tsconfig.app.json.
+       */
+
+      tsConfigPath = getTsConfigPath(tree, projectName, 'tsconfig.json');
+      tsConfigContent = getTsConfigContent(tree, tsConfigPath);
+    }
 
     tsConfigContent.exclude = [
       ...(tsConfigContent.exclude || []),