localization: update German translation (#1524)

- "Integrationen" is more common and modern than "Einbindungen"
- Replaced the word "Graph" with "Verlauf" because for the users it is quite synonymous
- Aligned issue tracker samples wording
- Use the more direct translation "System-Prompt" as it is a recognized term in German developer slang
- Aligned the use of words if similar words are used already or the context uses another word for the same thing
- Some grammar fixes

Author: warappa