fix: prevent thread panic on large tag values using postgres

Exceptionally large tag values (thousands of characters) can result in
an error from postgres: index row size exceeds btree version 4 maximum
2704 for index "tag_value_idx".  This panics the writer thread, and
prevents further writes from succeeding.

This change simply removes the unwrap, allowing the error to propagate
where it is sent as a write error back to the client.  The error
message could be improved.

scsibug#196

src/repo/postgres.rs

@@ -187,17 +187,15 @@ ON CONFLICT (id) DO NOTHING"#,
                                 .bind(tag_name)
                                 .bind(hex::decode(tag_val).ok())
                                 .execute(&mut tx)
-                                .await
-                                .unwrap();
+                                .await?;
                         } else {
                             sqlx::query("INSERT INTO tag (event_id, \"name\", value, value_hex) VALUES($1, $2, $3, NULL) \
                     ON CONFLICT (event_id, \"name\", value, value_hex) DO NOTHING")
                                 .bind(&id_blob)
                                 .bind(tag_name)
                                 .bind(tag_val.as_bytes())
                                 .execute(&mut tx)
-                                .await
-                                .unwrap();
+                                .await?;
                         }
                     }
                     None => {}