BaseRestartWorkChain let handler_overrides also override priority

[sphuber]

Currently the handler_overrides input allows to enable or disable certain error handlers that are defined on a work chain. There might be use cases where users may want to change the priority of handlers. Currently the form of the input is as follows

handler_overrides = {
    'handler_one': False,
    'handler_two': True,
}

We could add support for more keywords, but would have to go through a deprecation pathway:

handler_overrides = {
    'handler_one': {'enable': False, 'priority': 100},
    'handler_two': {'enable': True, 'priority': 200},
}