Remote Content Browsing: Replace indeterminate downloading loader by determinate on a content page

[MisRob]

A follow-up to https://github.com/learningequality/kolibri/pull/10558

Blocked by

#10391 #10564

Summary

When downloading remote content on a content page, we currently display an indeterminate loader (related PR https://github.com/learningequality/kolibri/pull/10558):

This should be replaced by a determinate loader (decision reference) as soon as backend can provide us with granular progress data (#10391)

Reported as a separate issue from #10564 since we agreed for the determinate loader version to be a stretch goal.