Added additional graph for total app instances in Diego.
Added additional graph for total app instances in Diego.

[#106138220](https://www.pivotaltracker.com/story/show/106138220)

Signed-off-by: Jim Park <7187dadeaa9825054bf26bb1a84055243400af16@pivotal.io>

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