Implement T&Cs acceptance client-side

[mmmarcos]

• On the enrollment screen, a checkbox should be added, indicating "I accept the CGU". => UI 0.5h.j
• The enrollment process is blocked as long as the checkbox is unchecked (i.e. "Next" button is disabled).
• On this same screen, a link must be added to the CGU (e.g. a static file added to the Parsec server). => UI 0.5h.j
  • CGU are server configured, not organization
• Parsec client retrieves link configuration from backend. => 2h.j
• Displays the checkbox only if a link to the CGU is present (backend link configuration). => UI 1h.j
• Information of date of acceptance should be sent to the server
• Add link on Menu for CGU to be able to read it at anytime. => UI 1h.j

[Max-7]

Depends on #7632