use Spring-Props for CORS-config, move CORS-config to BaseWebSecurityConfig and add tests (#212)

Co-authored-by: Michael Hoennig <michael@hoennig.de>
Reviewed-on: https://dev.hostsharing.net/hostsharing/hs.hsadmin.ng/pulls/212
Reviewed-by: Marc Sandlus <hsh-marcsandlus@noreply.dev.hostsharing.net>

src/main/resources/application.yml

@@ -70,6 +70,8 @@ spring:
 hsadminng:
     postgres:
         leakproof:
+    cors:
+        allowed-origin: ${ALLOWED_ORIGINS} // for compatibility with env-based CORS-configuration
 
 metrics:
     distribution: