Supports outOfSession via integration option & logEvent

[ladanazita]

Out-of-session events are not considered part of the current session, meaning they do not extend the current session. This might be useful if you are logging events triggered by push notifications, for example.

This supports calling logEvent with outOfSession passed in as true if the integration specific option is passed in: integrations.amplitude.outOfSession

There are four ways to log an event in Amplitude:

• Log event with props, groups and out of session flag
• Log event with props and groups
• Log event with props and out of session flag
• Log event with props

[f2prateek]

See the check for groups above and how it is retrieved. We need the same here.

[ladanazita]

@f2prateek made those changes!

[f2prateek]

Code is ok and we can merge it.

However, we might be able simplify the code branches a fair bit. We should do this in a follow up PR.

Internally it's likely that Amplitude's logEvent methods call each other with default arguments.

in analytics-ios track:@"foo" internally just calls track:@"foo" properties:nil which itself just calls track:@"foo" properties:nil options:nil.

So instead of having multiple branches like:

if properties != nil && options != nil {
  [analytics track:@"foo" properties:properties options:options];
} else if options == nil && properties != nil {
  [analytics track:@"foo" properties:properties];
} else {
  [analytics track:@"foo"];
}

You can just do:

[analytics track:@"foo" properties:properties options:options];

and internally the library handles all those cases.

The Android one does something similar to reduce the number of branches.