Add VCAP_SERVICES_FILE_PATH support

[kiril-keranov]

Adding support for VCAP_SERVICES_FILE_PATH, more info can be found here.
The feature usage demand is increasing as the current limitation of 130KB maximum content for VCAP_SERVICES is quite insufficient in various cases. The maximum content with VCAP_SERVICES_FILE_PATH is increased to 1MB.

The feature can be used when an application applies the following in the manifest:

features:
  file-based-vcap-services: true

Note: VCAP_SERVICES and VCAP_SERVICES_FILE_PATH are mutually exclusive as can be seen in the cloud controller code

[ramonskie]

this seems like a great feature and should be added to all the other buildpacks as well.
as currently no communitu buildpacks support this.
but it is documented