Expand the selectable Memory Sizes for small functions

[QuintinBecker]

Hey everybody,

corrently we are using Noobaa-Function to handle a small process for each file created in Storage. As these functions only consume some mb of memory we would like to scale down the reservation for each process to enable on endpoint to handle more tasks simulataniously without hitting the memory limits of the container.

We would like to extend the list of selectable "Memory Sizes" for a function to get called. Some tests were performed by setting the Memory Limits to lower values by hand with good performance improvements for small file uploads. Currently on endpoint is handling approxiamtely 30 trigger befor starting to drop, after adoption we had no issues any more for the test setup (Bulk upload of 150 files with size smaller 1mb). Runtime of each function in this case is under 2 seconds for getting access to an external service and handle the request.

[jeniawhite]

@QuintinBecker I've attached the relevant people to review your contribution. Thank you!