lambda defaults

taken from https://github.com/axiomhq/axiom-cloudfront-lambda/pull/13

@a-khaledf :
> Default lambda Memory allocation is 128MB, I am afraid if we are batching 10000 events that might sometimes lead to memory exceeding which would crash the lambda function. if we are doing that I would say let's make the batching configurable and add note that memory allocation should be increased relevant to the batching configuration

@seiflotfy:
> I tried it already and did some backfilling. memory did not exceed and I was hitting the 10k. But you might be right...
> I am making it configurable...
> However if we are doing multiple request back to axiom because of the batch sizes I don't think the default 300ms TTL of lambda would suffice!
> WDYT?

Start by reviewing the discussion in the issue and the referenced pull request 13, since no source files or tests are named. Clarify the intended configurable batching and the interaction with Lambda memory and request timing; done should include an agreed configuration and documentation of its operational limits.

Written by the indexing model from the issue text.