bug: correct `self` link in sub-communities endpoint

[carlinmack]

In subcommunities/services/service.py we have:

self_link = LinksTemplate(
    # https://github.com/inveniosoftware/invenio-communities/issues/1218
    # pagination_links("{+api}/communities/{community_id}/subcommunities{?args*}"),
    pagination_links("{+api}/communities/{community_id}/subcommunities"),
    context={"community_id": id_},
)
subcommunities._links_tpl = self_link

because the self_link returned from searching is not the subcommunities endpoint. As such we (improperly) directly replace the private _links_tpl with our own — however we do not have access to the correct args meaning that the self link, which could be subcommunties?p=1&size=10 will always return subcommunities as we don't have access