Add Documentation for ACTION_DEBUG_EVENT

The debug event action lost out on the documentation
for DebugEventReporter when it migrated to TM. This
change adds documentation for ACTION_DEBUG_EVENT
EXTRA_DEBUG_EVENT_ID, and EXTRA_DEBUG_EVENT_DESCRIPTION

Bug: 126178766
Test: make offline-sdk-docs (docstring-only change)
Change-Id: I6073d8b181c1258dbd7b47e8d5a45732d619396a