LogService: Retrieve dump generated by Manager

Adds support for retrieving the dump file that's generated by
phosphor-debug-collector as a result of using the LogServices/Dump
Action LogService.CollectDiagnosticData from the bmc Manager resource.

Refactors the handling for
/redfish/v1/Systems/<str>/LogServices/EventLog/Entries/<str>/attachment
to use one of the new functions and remove the large lambda.

Tested:
I began the dump generation process by sending a POST request to
/redfish/v1/Managers/bmc/LogServices/Dump/Actions/LogService.CollectDiagnosticData.
That spawned a Task to track the dump being generated by
phosphor-debug-collector.  The dump was retrieved by querying the
/redfish/v1/Managers/bmc/LogServices/Dump/Entries/<str>/attachment URI
which is associated with the Task.

Verified that an event log returned by querying
/redfish/v1/Systems/<str>/LogServices/EventLog/Entries/<str>/attachment
is the same as it was before this change.

Signed-off-by: Carson Labrado <clabrado@google.com>
Change-Id: I352b2628a9990bbde40f22e6134f02c89189c925
diff --git a/redfish-core/include/redfish.hpp b/redfish-core/include/redfish.hpp
index 3d8dae9..540bb07 100644
--- a/redfish-core/include/redfish.hpp
+++ b/redfish-core/include/redfish.hpp
@@ -144,6 +144,7 @@
         requestRoutesBMCDumpService(app);
         requestRoutesBMCDumpEntryCollection(app);
         requestRoutesBMCDumpEntry(app);
+        requestRoutesBMCDumpEntryDownload(app);
         requestRoutesBMCDumpCreate(app);
         requestRoutesBMCDumpClear(app);