[Reporters] Get theme from a config file

[RENARD Laurent]

For now, the theme is harcoded in the code. Ideally we want the user to be able to load its custom theme from a simple json file. This will allow for example to address accessibility issues (for visually impaired users)

ex:

I have a zora.theme.json in my project root

{
    "version":1,
     "bgError":"bgRed"    
}

Where the values can be anything in colorette

The zr binary should be able to load the file automatically based on the conventional name, or from a path configured by a cli parameter, etc