Add missing data-hook on customer_returns tab

[fkoessler]

This missing data-hook will help people trying to customize the orders tab with Deface.

Without the data-hook, there is no way to select the customer_return tab to replace or remove it.

This is my first pull request on solidus, I think I followed the contributing guidelines, let me know if I can improve the PR.

[kennyadsl]

Deface usage is not something we'd like to continue to encourage but staying consistent with other links here makes sense for me.

[gmacdougall]

Thanks for the contribution!