Add explicit timeout to mysql DB queries

docker/backend/mempool-config.json

@@ -60,7 +60,8 @@
     "PORT": __DATABASE_PORT__,
     "DATABASE": "__DATABASE_DATABASE__",
     "USERNAME": "__DATABASE_USERNAME__",
-    "PASSWORD": "__DATABASE_PASSWORD__"
+    "PASSWORD": "__DATABASE_PASSWORD__",
+    "TIMEOUT": "__DATABASE_TIMEOUT__"
   },
   "SYSLOG": {
     "ENABLED": __SYSLOG_ENABLED__,

docker/backend/start.sh

@@ -64,6 +64,7 @@ __DATABASE_PORT__=${DATABASE_PORT:=3306}
 __DATABASE_DATABASE__=${DATABASE_DATABASE:=mempool}
 __DATABASE_USERNAME__=${DATABASE_USERNAME:=mempool}
 __DATABASE_PASSWORD__=${DATABASE_PASSWORD:=mempool}
+__DATABASE_TIMEOUT__=${DATABASE_TIMEOUT:=180000}
 
 # SYSLOG
 __SYSLOG_ENABLED__=${SYSLOG_ENABLED:=false}