Improve hint UX for delete blob modal

The following discussion from !66872 (merged) should be addressed:

@himkp: Codewise this looks good but I think we can do a better job in terms of UX. We already have such a functionality in Web IDE commit box, can we try to reuse that?

The relevant code is in app/assets/javascripts/ide/components/commit_sidebar/message_field.vue

This is what it looks like:

More info

This is how our hint currently looks like: