Filter out cancellation exceptions for RUM errors

[StylianosGakis]

Context:
DataDog/dd-sdk-android#2426 (comment)

Tested by adding an interceptor which cancels all requests

    val okHttpBuilder = get<OkHttpClient.Builder>().addInterceptor(get<AuthTokenRefreshingInterceptor>())
      .addInterceptor {
        it.call().cancel()
        it.proceed(it.request())
      }

and seeing what that error looks like for the event mapper.
Then we simply drop the error event as suggested in the linked discussion