start-odk.sh memory calculation does not support cgroups v2

[spwoodcock]

Issue

• A made a commit a while ago to determine the total memory in the container using cgroups v1.
• This fix works fine for containers running cgroups v1, but does not work for cgroups v2.
• The version used is primarily determined by the host OS.
• I made a bit of an oversight, as my machine uses cgroups v1, but v2 is increasingly common. More info for Docker and Kubernetes.
• In scenarios where cgroups v2 is used, we get the following error (although the server still starts correctly):
  

Solution

• The script should handle both scenarios.
• It's easy enough to determine the cgroup version.

[matthew-white]

Closed by #876.