level detection: extracting level from nested json

[ashwanthgoli]

Describe the bug

Level detection currently only looks at the top level keys of a json for level or serverity keys. It fails to extract level information from nested fields. Even the fallback that searches the log line for level tokens does not handle all scenarios.

Following log line for example does not get detected as warn since this function detectLevelFromLogLine is not exhaustive.

{
    "body": {
        "message": "foo",
        "level": "warn"
    }
}