Disable CSRF protections

Partially reverts #59
CORS is configurable via yaml config files, CSRF is not.

From my understanding, CSRF protection has to be managed separately by
the underlying webapps being proxified by the gateway.

gateway/src/main/java/org/georchestra/gateway/security/GatewaySecurityConfiguration.java

@@ -74,6 +74,10 @@ SecurityWebFilterChain securityWebFilterChain(ServerHttpSecurity http,
 
         log.info("Initializing security filter chain...");
 
+        // disable CSRF protection, considering it will be managed
+        // by proxified webapps, not the gateway.
+        http.csrf().disable();
+
         http.formLogin()
                 .authenticationFailureHandler(new ExtendedRedirectServerAuthenticationFailureHandler("login?error"))
                 .loginPage("/login");