Migrate StringCodec configuration during upgrade to 12.2

Create a migrator that moves the StringCodec configuration from /hippo:configuration/hippo:frontend/cms/cms-services/settingsService/codecs to the new location in /hippo:configuration/hippo:moduleconfig. See https://www.onehippo.org/library/concepts/content-repository/node-name-encoding.html for details on the old configuration. Goal: a custom node name codec should still work fine in 12.1.