Improve redundancy of nexus repo to avoid timeouts

[djtfmartin]

Investigate ways to improve the redundancy of the nexus repo. Timeouts are a big problem for the ansible scripts for folks running outside of Australia. The timeouts from access to ALA's nexus repository.

GBIF do mirror artefacts, but there is a delay (and it currently requires a config switch to use the GBIF repo instead of the ALA repo).

[ansell]

Refs https://github.com/AtlasOfLivingAustralia/maintenance/issues/35