Adds graph for open file descriptors per vm
Adds graph for open file descriptors per vm

- Aggregates by sum instead of avg for overall open FDs per component

[#119550955]

Signed-off-by: Warren Fernandes <5224037f27468fce7f4daf7074f39274a32f90c2@pivotal.io>

pivotal-cf-experimental/datadog-config-oss,pivotal-cf-experimental/datadog-config-oss