This commit adds multiple repositories support to get snapshots
request.
If some repository throws an exception this method does not fail fast
instead, it returns results for all repositories.
This PR is opened in favour of #41799, because we decided to change
the response format in a non-BwC manner. It makes sense to read a
discussion of the aforementioned PR.
This is the continuation of work done here #15151.
680d6edc0b