requester: Modified MctpDiscovery class

Modified MctpDiscovery class to take list of managers instead of single
fwManager. The change is for adding platform-mc manager.
Added loadStaticEndpoints API for MCTP layer which doesn't implement
/xyz/openbmc_project/MCTP/Endpoint.Interface

The patch is part of implementation of design document below.
https://gerrit.openbmc-project.xyz/c/openbmc/docs/+/47252



Signed-off-by: Gilbert Chen <gilbert.chen@arm.com>
Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
Change-Id: I1e1673504583a87f2a9bc3adf76fb49c2dc30254