Add backend/libs/network-modification (#11)

Author: jonenst

.gitmodules

@@ -393,3 +393,8 @@
 	url = https://github.com/gridsuite/user-identity-oidc-replication-server
 	branch = main
     ignore = all
+[submodule "backend/libs/network-modification"]
+	path = backend/libs/network-modification
+	url = https://github.com/gridsuite/network-modification
+	branch = main
+    ignore = all

backend/libs/network-modification

@@ -22,6 +22,7 @@
 
     <modules>
         <module>filter</module>
+        <module>network-modification</module>
         <module>powsybl-case-datasource</module>
         <module>powsybl-core</module>
         <module>powsybl-diagram</module>