mctpd: use new Bus Owner name of `au.com.CodeConstruct.MCTP`

[jk-ozlabs]

We currently use a Bus Owner name of xyz.openbmc_project.MCTP, to suit conventions with the existing dbus interface names, and MCTP object path structure.

However, mctpd is not under the OpenBMC umbrella, so we should be using our own namespace instead.

Change to a Bus Owner value of au.com.CodeConstruct.MCTP, but keep the old value for compatibility. This will be removed in a future release, once we have confidence that consumers are using the new name.

[jk-ozlabs]

Per some conversation on the OpenBMC discord, we may want to use this as an opportunity to implement a more comprehensive (and versioned) dbus object model.

[amboar]

(for the record, the conversation happens around here: https://discord.com/channels/775381525260664832/778790638563885086/1240142924381945856)

[jk-ozlabs]

Closed by #43