staging: Deploy apache service to serve extracted export.fld files

One per maven repository listed.

Related to T3746 Depends on !505 (closed)

Test Plan

vagrant provision staging-maven-indexer

Start a service that computes the fld and move the fld file to the apache service to serve it:

# from within the vagrant vm
root@maven-exporter0:~# systemctl start maven_index_exporter@clojars.service
root@maven-exporter0:~# curl -s -k https://maven-exporter.internal.staging.swh.network/export-clojars.fld | head
doc 0
  field 0
    name u
    type string
    value lein-environ|lein-environ|1.1.0|NA|pom
  field 1
    name m
    type string
    value 1647205295753
  field 2

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Migrated from D7528 (view on Phabricator)