[Feature]: allow overriding machine default values.

[janek202]

Is your proposal related to a problem?

Currently it's possible to change the type of the machine, but some parameters are always hardcoded:
MAC_OPTS="-machine type=${MACHINE},smm=${SECURE},graphics=off,vmport=off,dump-guest-core=off,hpet=off${KVM_OPTS}"

In some cases, these options, may be incompatible with the Guest OS, which may require HPET, or vmport.

Describe the solution you'd like.

A new env variable, such as MACHINE_OPTS/MACHINE_DEFAULT_OPTS with a default value of graphics=off,vmport=off,dump-guest-core=off,hpet=off which could be overriden in a Dockerfile, as needed.

Describe alternatives you've considered.

I'm not sure if there's a way to override it in any other way.

Additional context

No response