⚡️(backend) change db state instead of using long running row lock

When analysing a file, the previous commit introduced a row level lock
to make sure we would analyse and promote a single file.
This commit changes the locking mechanism so that it happens with
the upload state which avoids long running db locks and potential
perf issues.

src/backend/core/models.py

@@ -846,8 +846,8 @@ class FileUploadStateChoices(models.TextChoices):
     """Possible states of a file."""
 
     PENDING = "pending", _("Pending")
+    ANALYZING = "analyzing", _("Analyzing")
     # Commented out for now, as we may need this when we implement the malware detection logic.
-    # ANALYZING = "analyzing", _("Analyzing")
     # SUSPICIOUS = "suspicious", _("Suspicious")
     # FILE_TOO_LARGE_TO_ANALYZE = (
     #     "file_too_large_to_analyze",