Translate 404, 500, 422 errors pages

[jibees]

What? Why?

Closes #9492

What should we test?

• The aim is to test the errors page, they should be the same as previous by default, and can now be translated via keys:
  • .errors.(not_found|internal_server_error|unprocessable_entity).title for the title,
  • .errors.(not_found|internal_server_error|unprocessable_entity).message_html for the content of the page
• Errors pages can be access via /404, /500 and /422 and I can imagine that they should be displayed if any errors (type 404, 500, 422) occurs.

Release notes

Changelog Category: User facing changes