Allow arbitrary MySQL JDBC connection properties in config.yml

storage.mysql.properties is now a free-form map merged into the JDBC
URL as ?key=value&key=value..., letting hosts that require TLS set
things like sslMode: REQUIRED, or override the useSSL/autoReconnect
defaults, without needing a code change for every possible parameter.

stargate-paper/src/main/resources/config.yml

@@ -17,6 +17,15 @@ storage:
     username: stargate
     password: ""
     table-prefix: "stargate_"
+    # Extra JDBC connection parameters, appended to the URL as ?key=value&key=value.
+    # Defaults to useSSL: false and autoReconnect: true if you don't set them here -
+    # any key you list overrides that default (e.g. set useSSL: true and add sslMode
+    # to actually require TLS). Values are written into the URL as-is.
+    properties:
+      # useSSL: true
+      # sslMode: REQUIRED
+      # serverTimezone: UTC
+      # allowPublicKeyRetrieval: true
 
 # Enables sending players to another backend server when they dial a gate whose
 # server-id differs from this one. Requires the stargate-velocity or stargate-bungee