JSON output: flatten levels

[maria-messerschmidt]

The JSON output has a few redundant levels and would be easier to parse if the messages were structured as a flat array within each report.

Currently, this is the structure of the "messages" objects. I have marked with bold the levels that could be flattened. The "package" and "mimetype" objects can either be moved to the message level (as shown in the example below) or even to the parameters level (see #227).

{
"messages":{
"messages":{
"package":[
{
"id":"DOC-2",
"severity":"INFO",
"message":"OpenDocument version 1.3 detected.",
"subMessage":"",
"timestamp":"2025-01-17 07:03 UTC"
}
],
"mimetype":[
{"id":"DOC-3",
"severity":"INFO",
"message":"OpenDocument MIMETYPE .[..]..detected",
"subMessage":"",
"timestamp":"2025-01-17 07:03 UTC"
}
]
},
"warning_count":0,
"info_count":2,
"error_count":0
}
}

And the result would be something like this:

{
"messages":[
{
"location": "package",
"id":"DOC-2",
"severity":"INFO",
"message":"OpenDocument version 1.3 detected.",
"subMessage":"",
"timestamp":"2025-01-17 07:03 UTC"
}
{
"location": "mimetype"
"id":"DOC-3",
"severity":"INFO",
"message":"OpenDocument MIMETYPE .[..]..detected",
"subMessage":"",
"timestamp":"2025-01-17 07:03 UTC"
}
]
"warning_count":0,
"info_count":2,
"error_count":0
}