[native] Send PONG when PING is received

Summary:
Check background notification type and react accordingly

Depends on D3133

Test Plan:
Send a background notification on Android and check if the code on C++ was executed

{
  data: {
    backgroundNotifType: 'PING',
  },
}

Reviewers: karol-bisztyga, ashoat, atul, jimpo

Reviewed By: karol-bisztyga, ashoat

Subscribers: benschac, ashoat, Adrian, atul

Differential Revision: https://phabricator.ashoat.com/D3134