shipit/api: add ESR_NEXT in primary_builds.json (#2213)
shipit/api: add ESR_NEXT in primary_builds.json (#2213)

When we have 2 ESR releases active at the same time, we want them both
to be in `firefox_primary_builds.json`
La0/mozilla-relengapi,La0/mozilla-relengapi,mozilla-releng/services,mozilla-releng/services,La0/mozilla-relengapi,La0/mozilla-relengapi,mozilla-releng/services,mozilla-releng/services