Update sample app to test new Sentry features

[wzieba]

Description

This PR adds a few changes to the sample app that allow to test #269

Testing

Before tests cp gradle.properties-example gradle.properties and set a valid sentryTestProjectDSN (tracks-demo-android project on A8c Sentry.

isAttachAnrThreadDump

1. Install the app in release
2. Tap "Force ANR"
3. See a new Sentry issue reported. I couldn't find any additional data regarding ANR thread dump, but that's likely it's a very simple stacktrace from the sample app - I guess in production apps, in more complex scenarios we'll have some data on this.

isStartProfilerOnAppStart

1. Go to https://a8c.sentry.io/profiling/?project=6626116&statsPeriod=24h&tab=flamegraph
2. In the bottom right corner see the last id of a profile
3. Run the sample app
4. Wait a few seconds, refresh the UI a few times
5. See that there's a new profile available.

Image

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☝️ a sampling trace from a test method I've added (it waited 3s on the main thread).

[ParaskP7]

👋 @wzieba !

I have reviewed and tested this PR as per the instructions, everything works as expected, thanks for the thorough testing instructions and TIL on tracks-demo-android, this makes testing so much easier for me! 🧪 x 🧪 ^ 🧪

isAttachAnrThreadDump
...
3. See a new Sentry issue reported. I couldn't find any additional data regarding ANR thread dump, but that's likely it's a very simple stacktrace from the sample app - I guess in production apps, in more complex scenarios we'll have some data on this.

👍

isStartProfilerOnAppStart
...
5. See that there's a new profile available.

👌