Use FaultLogType converter and introduce new MetisCPER type

Change phosphor-debug-collector to support any legal CPER enum type,
without code patching. Introduce a new MetisCPER type. Add a test to
show createDump() works as expected. Added docs for new CPER type.

Tested: Unit tests pass (dump_manager_faultlog_test). Verified BitBake
build and passing Mimik presubmit on agentless platforms.
Fusion-Link: http://fusion2/ae82e2c3-1c59-3277-a79f-7b485962268b
Google-Bug-Id: 465785138
Change-Id: I40cb7ae43be43620c565fe48a261aac0fb372c65
Signed-off-by: Ron Vered <ronvered@google.com>