feat: make as optional the langage selection by configuration

Please, create one MR for each new feature, don't submit multiple new features at once, unless they are very tied.

What does it do?

Define a configuration property to hide the Langage Selector. The option permit to avoid that users change the lang defined by default.

Is there a related issue?

What part of MyPads are modified?

• backend
• frontend

Check list

• did you squash your commits?
• did you respect the coding guidelines?
• did you add new translations key?
• did you add new tests