L2SS-251: SKA Tango images moved

Closes L2SS-251

See merge request !54

Any images missing from the artefact.skatelescope.org registry are now
configured to be downloaded from git.astron.nl:5000

This patch ensures all images available from artefact.skatelescope.org
are pinned to a specific version. This is necessary as :latest is not
available on this registry.

L2SS-251: Refer to the DOCKER_REGISTRY environment variables in .env for source images, instead of hard-coding them in the Dockerfiles

L2SS-199: Remove asyncua requirement as it's unused. Upgrade opcua lib requirement to 0.98.13.

Closes L2SS-199

See merge request !52

Resolve L2SS-230 "Add sdp sim"

Closes L2SS-230

See merge request !48

Resolve L2SS-246 "Capitalise sdp"

Closes L2SS-246

See merge request !51

L2SS-232: Add a Docker tag/push script for local images

Closes L2SS-232

See merge request !49

L2SS-225:  Fix rebuild_system_from_scratch.sh to also function on CentOS7

Closes L2SS-225

See merge request !41

L2SS-229 "Add gitpython and python-logstash-async to itango"

Closes L2SS-229

See merge request !46

L2SS-231: add a device with 20 attributes that generate random numnbers on read

Closes L2SS-231

See merge request !47

L2SS-192: Provide interface for raw header fields, add example packet (needs...

Closes L2SS-192

See merge request !45

L2SS-192: reserved_0 -> reserved to not be overly defensive. if there are multiple reserved fields in the future, we'll deal with that by then.

L2SS-228: Fix mount path for the host's tango repo dir to /opt/lofar2.0/tango/

Closes L2SS-228

See merge request !44

L2SS-170:  First stab at an LTS cold start script

See merge request !22