docs(logger): add loglevel trace to documentation (aws-powertools#1589)

Author: timo92

Diff for: docs/core/logger.md

@@ -454,6 +454,7 @@ We support the following log levels:
 
 | Level      | Numeric value |
 | ---------- | ------------- |
+| `TRACE`    | 6             |
 | `DEBUG`    | 8             |
 | `INFO`     | 12            |
 | `WARN`     | 16            |