PIM-2517 : introduce a _index_buttons template to ease overriding

| Q                    | A
| -------------------- | ---
| Bug fix?             | N
| New feature?         | Y (partialy)
| BC breaks?           | N
| CI currently passes? | Y
| Tests pass?          | Y
| Scenarios pass?      | ?
| Checkstyle issues?*  | N
| PMD issues?**        | N
| Changelog updated?   | N
| Fixed tickets        | PIM-2517 (partialy)
| Doc PR               |