Implement changes to enable native modules auto linking (facebook#24506)

Summary:
Replaces facebook#24099 (original PR became detached for some reason)

Implements the template changes required to enable native modules auto-linking for both Android & iOS.

Requires the following to be merged first and an updated CLI to be published:

- [x] react-native-community/cli#254
- [x] react-native-community/cli#256
- [x] react-native-community/cli#258

cc grabbou thymikee orta for review

- [ ] facebook#24517 update CLI version)

[TEMPLATE] [FEATURE] - Enable auto-initialization/linking of react native modules for new projects
Pull Request resolved: facebook#24506

Differential Revision: D15062701

Pulled By: cpojer

fbshipit-source-id: 65296cbec2925405fe8033de71910325e0c719bc

# Conflicts:
#	template/ios/Podfile

Author: Salakar

template/ios/Podfile

@@ -1,4 +1,5 @@
 platform :ios, '9.0'
+require_relative '../node_modules/@react-native-community/cli-platform-ios/native_modules'
 
 target 'HelloWorld' do
   # Pods for HelloWorld
@@ -32,6 +33,7 @@ target 'HelloWorld' do
     # Pods for testing
   end
 
+  use_native_modules!
 end
 
 target 'HelloWorld-tvOS' do