Resolve "[Docker] Do not run as root"

Closes #409

See merge request !544

Update dependency django-haystack to v3.0

See merge request !548

Update dependency django-colorfield to ^0.4.0

See merge request !547

Run poetry update

See merge request !545

Previously, we relied on either explicit configuration to place the
file in a writable location, or the webserver being able to write to
the source tree.

With a (probably even replicated) setup where nothing runs as root,
and al lstorages are thus read-only except for the media storage, we
need to put the maintenance file there.

Advances #403

Advances #403

Advances #403

[Docker/K8s] Fix typo in S3 storage class name

See merge request !542

Resolve "Support S3 storage for media"

Closes #405

See merge request !534

Update DjDT to 3.2

See merge request !541

Resolve "Use django-guardian's prefetch mechanism for object permissions"

Closes #407

See merge request !540