feat: Toggle for JSON pretty printing

[vonhoff]

Feature Request: Pretty-Printed JSON Output for RichTextBox Sink

Detailed Description

The current JSON value formatter outputs all structured values in a single-line, compact JSON format. This is ideal for dense log streams, but when logs are viewed in a UI, compact JSON can be difficult to visually scan, especially for nested objects or arrays.

It would be useful to have an option to format structured values as pretty-printed, multi-line JSON, with indentation and line breaks.

Expected behavior

Example compact output (current behavior):

{"User":"Simon","Roles":["Admin","Maintainer"],"Active":true,"Score":9.7}

Proposed pretty-printed mode:

{
    "User": "Simon",
    "Roles": [
        "Admin",
        "Maintainer"
    ],
    "Active": true,
    "Score": 9.7
}