storage*: Type origin_search(...) -> PagedResult[Origin]

This unifies the how the pagination is now done, abstracting away how the pagination is dealt with internally.

This does not touch the internal logic of limit/offset used within.

Impacts swh-web:

grep -r 'origin_search(' ../*/swh/** | grep -v "swh-storage" | grep -v "swh-search"
../swh-web/swh/web/api/views/origin.py:def api_origin_search(request, url_pattern):
../swh-web/swh/web/common/service.py:        results = search.origin_search(
../swh-web/swh/web/common/service.py:        origins_raw = storage.origin_search(
../swh-web/swh/web/assets/src/bundles/browse/origin-search.js:    baseSearchUrl = new URL(Urls.api_1_origin_search(searchQueryText), window.location);
../swh-web/swh/web/tests/api/views/test_origin.py:def test_api_origin_search(api_client, mocker, backend):

Related to T645

Test Plan

tox

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Migrated from D3651 (view on Phabricator)