Batch send log items

[antonpirker]

In the current PoC each log statement triggers the sending of an envelope. This should be changed.

We should wait for X seconds or Y log items being collected until we create one envelope containing all the available log items and send them to Sentry.

Should work similar as it works/worked for metrics or sessions.

We should also think about having just one thread that collects different kind of data items and sends them to Sentry. Because we already create some threads in the SDK and we sometimes already hit the limits of environments in regard of maximum numbers of threads allowed (in AWS Lambda this is already a problem)