Enhance search function in Communication

[dfuchss]

Is your feature request related to a problem?

We rely on a working search function. Nevertheless, simple search is not working (see example below)

Describe the solution you'd like

Especially in large courses with many students, the students and instructors rely on a good search function to easily find related threads. Nevertheless, the search function is not reliable.

Simple example: If I search for "Random" I'd expect that a message like "Das Aufgaben-Dokument erwähnt, dass der Konstruktor Random(long) für den Pseudozufalls...." should be found. Nevertheless, this is not the case.

A possible option would be the use of a search index like apache solr: https://solr.apache.org/guide/solr/latest/deployment-guide/solrj.html or elastic search https://www.elastic.co/guide/en/elasticsearch/client/java-api-client/current/index.html

Describe alternatives you've considered

No response

Additional context

No response](https://solr.apache.org/guide/solr/latest/deployment-guide/solrj.html)