maven: add index nginx host in docker dev setup

Adds a container to the docker-dev setup to run a nginx server to host the extracted maven index file. This "external" server is required to run the maven-lister. The served directory is in conf/maven-index, feel free to use any fld file instead.

Command used to run the lister:

swh scheduler task add  list-maven-full url=https://repo1.maven.org/maven2/ index_url=http://swh-lister-maven-nginx/export.fld

Related to T1724

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Migrated from D6955 (view on Phabricator)