Add Bolt TLS termination as optional feature

compose.yaml

@@ -41,6 +41,10 @@ services:
       BOLTAGE_PG_DATABASE: postgres
       BOLTAGE_DEFAULT_GRAPH: ${BOLTAGE_DEFAULT_GRAPH:-neo4j}
       BOLTAGE_LOG_LEVEL: ${BOLTAGE_LOG_LEVEL:-INFO}
+      # true: TLS with a self-signed certificate, kept in the boltage-tls volume.
+      BOLTAGE_TLS_SELF_SIGNED: ${BOLTAGE_TLS_SELF_SIGNED:-false}
+    volumes:
+      - boltage-tls:/var/lib/boltage
     ports:
       - "7474:7474"
       - "7687:7687"
@@ -67,3 +71,4 @@ services:
 volumes:
   postgres-data:
   pgadmin-data:
+  boltage-tls: