Old smesher image in system tests should use its own configuration file

[fasmat]

Description

In system tests we have smeshers that run the tested version and (some) smeshers that run an older released version to ensure that any changes we make don't break an existing network.

The way this is implemented at the moment causes some issues though because both versions of the node are expected to run with the same configuration and launch parameters, when this might not be possible because of forward compatibility issues. E.g. in #6652 new (optional) configuration parameters were added to the config file that were set in the system tests and prevented old smeshers from starting with that configuration.

Instead old smeshers should have their own configuration and launch parameters so we can still test compatibility between the newest and older versions of the node.

Affected code

Code in the systest package. Ideally after resolving this issue set the old smesher image back to v1.7.7 since this is the oldest version that we still expect to be compatible with the current spacemesh version.