Add config options for cors handling (#124)

Add config options for cors handling

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/124

docs/content/doc/setup/config.md

@@ -106,6 +106,15 @@ redis:
   # 0 means default database
   db: 0
 
+cors:
+  # Whether to enable or disable cors headers.
+  enable: true
+  # A list of origins which may access the api.
+  origins:
+    - *
+  # How long (in seconds) the results of a preflight request can be cached.
+  maxage: 0
+
 mailer:
   # Whether to enable the mailer or not. If it is disabled, all users are enabled right away and password reset is not possible.
   enabled: false