FR: Enable Performance session capturing for 100% of users in development

### [REQUIRED] Step 2: Describe your environment

* Xcode version: 10.1
* Firebase SDK version: 6.5.0
* Firebase Component: PerformanceMonitoring
* Component version: 3.1.1

### [REQUIRED] Step 3: Describe the problem

Create a new single-view app in Xcode
Follow the instructions to add Firebase to the app
https://firebase.google.com/docs/ios/setup

Follow the instructions to add FirebasePerformanceMonitoring to the app
https://firebase.google.com/docs/perf-mon/get-started-ios

Launch the app
Wait 12h
Look at the FirebaseConsole and try to access sessions for the performance logs
Sessions are not available, we are advised to update our SDK

#### Relevant Code:

[SampleFirebasePerf.zip](https://github.com/firebase/firebase-ios-sdk/files/3432267/SampleFirebasePerf.zip)

I removed podfiles and GoogleService-Info.plist, you will need to restore podfiles and add your own GoogleService-Info.plist to run the same.

Simply launch the app, wait 12h and look at the data on the console.