The shorttext value must be between 1 and 100 characters long

Problem/Motivation

A site using this module has hit a problem with the shorttext field because it is longer 100 characters.

 GuzzleHttp\Exception\ClientException: Client error: `POST https://tom.vgwort.de/api/external/metis/rest/message/v1.0/newMessageRequest` resulted in a `400 Bad Request` response:
{"errorField":"messagetext.shorttext","objectName":"newMessageRequest","message":"size must be between 1 and 100"}

Steps to reproduce

See a message with a shorttext longer 100 characters to VG Wort.

Proposed resolution

Truncate the short text to the nearest word boundary to 100 characters.

Remaining tasks

User interface changes

None

API changes

None

Data model changes

None