[web] Always send a language header in all requests

[exalate-issue-sync]

Description

Most of the translations happen in web itself. Notifications are about to be translated backend side, i.e. web will receive already translated content. We might provide translated error messages in the future. So it makes sense to always let the backend know about the language of the user.

User Stories

• As user i want to have a UI translated in my preferred language to understand it better

Value

Acceptance Criteria

• Web always sends a language header in all requests which follows the Accept-Language spec https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Language

Definition of ready

[ ] everybody needs to understand the value written in the user story
[ ] acceptance criteria has to be defined
[ ] all dependencies of the user story need to be identified
[ ] feature should be seen from an end user perspective
[ ] user story has to be estimated
[ ] story points need to be less then 20

Definition of done

• Functional requirements
  [ ] functionality described in the user story works
  [ ] acceptance criteria are fulfilled
• Quality
  [ ] code review happened
  [ ] CI is green
  [ ] critical code received unit tests by the developer
  [ ] automated tests passed (if automated tests are not available, this test needs to be created and passed
• Non-functional requirements
  [ ] no sonar cloud issues