Release 6.20.2: sms messaging api: optionally modify the RegEx used for eliminating characters

[changerequest]

It is now possible to define the RegEx which is used to eliminate characters silently. These characters will be removed from the input without any message before the result is sent to the backend.

Bundles extending
com.openexchange.messaging.sms.service.AbstractMes sagingUserConfigurationInterface
still get the old default.