Add support for setting a custom User-Agent

[cmelchior]

Closes #6267

This PR adds an optional parameter when calling Realm.init(). This will set the user part of the User-Agent string.

I'm using Realm.init() as people are only calling this once and we also initialize the SyncManager as part of calling it. The extra constructor is only visible when using a build supporting the Object Server.

// Usage
Realm.init(context, "MyApp/" + BuildConfig.VERSION_NAME);

The String constructed by RealmJava will look like this for e.g. OnePlus:

// Example of String for OnePlus
RealmJava/5.8.0-SNAPSHOT (OnePlus5T, ONEPLUS A5010, v27) ObjectServerExample/1.0

The server will output something like this:

// Server connection example from emulator
2018-11-02T10:52:30.103Z - info: [sync] Sync Connection[29]: Session[1]: Client info: (path='/9e896ae0c1ff90402bc978cab085659f/tests', user='9e896ae0c1ff90402bc978cab085659f', from=[127.0.0.1]:46980, protocol=25) RealmSync/3.13.1 (Android Linux 4.4.34-genymotion #1 SMP PREEMPT Mon Dec 5 15:49:16 UTC 2016 i686) RealmJava/5.8.0-SNAPSHOT (vbox86p, Custom Phone - 7.1.0 - API 25 - 768x1280_1, v25) ObjectServerExample/1.0

Specifically, we are sending

• Version name for RealmJava.
• Build.DEVICE
• Build.MODEL
• Build.VERSION.SDK_INT (named SDK is deprecated)

Build.PRODUCT sees to contain the same information as DEVICE/MODEL so doesn't look relevant.

@roberhofer Is this sufficient?

[roberhofer]

Great. Looking at the example provided it seems that all the relevent info is there, e.g.

• which platform (Android and version)
• which sync version, and binding.
  Appreciated.

[nhachicha]

I have one concern regarding appDefinedUserAgent it should be optional as explained in the feedback