Give a more helpful message on error

Before:

```
database error: ERROR: insert or update on table "owner_rels" violates foreign key constraint "owner_rels_cid_fkey"
```

After:

```
database error: ERROR: insert or update on table "owner_rels" violates foreign key constraint "owner_rels_cid_fkey"
DETAIL:  Key (cid)=(4) is not present in table "releases".
```

Author: jyn514

tokio-postgres/src/error/mod.rs

@@ -309,7 +309,14 @@ impl DbError {
 
 impl fmt::Display for DbError {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(fmt, "{}: {}", self.severity, self.message)
+        write!(fmt, "{}: {}", self.severity, self.message)?;
+        if let Some(detail) = &self.detail {
+            write!(fmt, "DETAIL: {}", detail)?;
+        }
+        if let Some(hint) = &self.hint {
+            write!(fmt, "HINT: {}", hint)?;
+        }
+        Ok(())
     }
 }