Add option to set a fixed max value for the scale of network charts

[victor-marino]

In the network charts, it would be great to have the option of fixing the scale manually, as many other apps allow us to do.

I've created #1746 as an initial implementation.

Among other things, this would allow us to use the network chart as a "utilization" chart, where the chart represents the % of bandwidth we're using out of the total available bandwidth in our internet connection.

A more detailed explanation of why this feature is useful can be found here.

The core logic is done with this PR and the chart plots the values as expected. However, there are some missing tweaks that I couldn't implement by myself due to lack of knowledge about MacOS development.

What's already implemented:

• New toggle to enable/disable the Custom Scale option
• New text field to enter the maximum desired bandwidth for the chart in Mbps (for now, a common value for DL and UL)
• Independent settings have been added for the widget and the pop-up charts
• Both charts will pick up the new value as soon as the text field is modified (if the toggle is enabled)

Still to do, hopefully with @exelban's help 😉 :

• Hide/disable the input text field when the toggle is disabled. Of course, up to @exelban to decide if he prefers an alternative behaviour. For instance, we could instead remove the toggle, and then:
  • Enable the feature if the user enters a bandwidth value
  • Disable the feature if the user leaves the text field empty
• Sanitize the input of the text field to allow only numerical digits
• Allow entering separate values for the download and upload speed

[victor-marino]

Thanks for this! Working great :)

What about the status bar widget? Any chance the scale can be fixed in there as well?

[exelban]

yeap, it will be added