feat: copy instances/endpoints info while updating mainsail/fluidd

[szafran81]

Is your feature request related to a problem? Please describe

Right now every update removes instances/endpoints configuration from config.json in both mainsail and fluidd.

Describe the solution you'd like

While updating read and copy to new config the instances configuration:

In mainsail (config.json):

    "instancesDB": "json",
    "instances": [
        { "hostname": "192.168.1.99", "port": 7125 },
        { "hostname": "192.168.1.99", "port": 7126 }
    ]

In fluidd (config.json):

  "endpoints": [
    "http://192.168.1.99:7125",
    "http://192.168.1.99:7126"
  ],

And I think there is a lot more info that can be copied with that. Maybe walking through the config and only copying from new config.json data that's been added and leaving old settings untouched?

Describe alternatives you've considered

Reconfiguring by manually editing config files after every update is such a waste of time.

Additional information

No response