Add CocoaPods Podfile to the project template (#23563)

Summary:
CocoaPods makes it easier to add new iOS dependencies to a project without having to manually edit Xcode projects. Editing Xcode projects is time consuming and merging changes to them difficult. Automating the changes to Xcode project `react-native link` is error prone. CocoaPods is a de-facto standard way to manage iOS dependencies and a central part of unimodules and upcoming improvements to `react-native link`.

This PR adds a `Podfile` to the default project template of React Native. To use a project with CocoaPods, after creating it, run `cd ios; pod install` and use the created `<projectname>.xcworkspace` file instead of the `.xcodeproj` file. (We could make this a part of `react-native init` so you only need to run one command when creating a project.)

[iOS] [Added] - Add CocoaPods Podfile to the project template
Pull Request resolved: #23563

Differential Revision: D14576505

Pulled By: cpojer

fbshipit-source-id: f6c9e93d61a52ad445d2931ccc4933d559a6ec1a

Author: fson

.gitignore

@@ -69,3 +69,7 @@ package-lock.json
 # ReactCommon subdir shouldn't have Xcode project
 /ReactCommon/**/*.xcodeproj
 RNTester/build
+
+# CocoaPods
+/template/ios/Pods/
+/template/ios/Podfile.lock

scripts/run-ci-e2e-tests.js

@@ -187,6 +187,8 @@ try {
       'response=$(curl --write-out %{http_code} --silent --output /dev/null localhost:8081/index.bundle?platform=ios&dev=true)',
     );
     echo(`Starting packager server, ${SERVER_PID}`);
+    echo('Running pod install');
+    exec('pod install');
     echo('Executing ' + iosTestType + ' end-to-end test');
     if (
       tryExecNTimes(() => {
@@ -204,6 +206,8 @@ try {
         return exec(
           [
             'xcodebuild',
+            '-workspace',
+            '"EndToEndTest.xcworkspace"',
             '-destination',
             `"${destination}"`,
             '-scheme',

template/_gitignore

@@ -54,3 +54,6 @@ buck-out/
 
 # Bundle artifact
 *.jsbundle
+
+# CocoaPods
+/ios/Pods/