Truncate stack trace in SNOWError

[matus-tomlein]

Currently the stack trace is unbounded which can result in events failing validation. We should clip it to a max length.

[plu]

https://github.com/snowplow/snowplow-objc-tracker/blob/master/Snowplow/Internal/Events/SPTrackerError.m#L72

There's some code that tries to clip the max length, but not sure all code paths go through this.

[matus-tomlein]

Hey @plu, you're right that the stack trace is truncated in the SPTrackerError event but it's not truncated in the SNOWError event.

The difference is that the SPTrackerError is tracked when tracker diagnostic autotracking is enabled. This includes log messages produced by the tracker.

On the other hand, the SNOWError is tracked when exception autotracking is enabled and it captures errors raised anywhere in the app code.