Setup golden DB in merge-ci

[joshmoore]

cc: @pwalczysko

[sbesson]

Added some notes capturing how this feature had been implemented in ci.openmicroscopy.org a few years back with @pwalczysko.

Minimally, this implementation can be seen as an extension of the PURGE_DATA option in devspace 0.11.0 as:

https://github.com/ome/devspace/blob/6e1187def58438e46feee33b624c7aa86405076c/home/jobs/OMERO-server/config.xml#L55-L60

In addition to these comamnds purging the database and the binary repository, a subsequent step is to restore an existing reference DB + binary repo. There are a few assumptions here:

• the database and the binary repo need to be available from the Jenkins environment

• the golden DB to be created in a systematic way (pg_dump format, disk layout)

• enough space need to be provisioned esp. for large valuable DBs. By default, the data directory is in the same place as the devspace clone.

  https://github.com/ome/devspace/blob/0b063775305b053b285d8a6fe913af0ecb5f7d9d/home/jobs/OMERO-server/config.xml#L19-L23

  Minimally, this variable would need to be overriden or the path on disk symlinked to a larger volume with appropriate write permissions.