Add pagination to full-text metadata search

Currently, full-text metadata search only returns the top results, with a limit to the number of results.

Someone who wants to do data mining on a subset of the metadata we store, which exceeds that limit. Therefore, we need to add pagination to these results, so more of them can be fetched.

This requires adding pagination to the indexer storage API and the webapp.

Migrated from T1614 (view on Phabricator)

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