Add option to enable use of TLS for connection to Redis

[rogu-beta]

Describe the bug
Currently PurlDB does not use TLS when connecting to Redis and does not offer an option to enable it. This is an issue when attempting to deploy PurlDB with Redis hosted on a separate system (e.g. a cloud deployment with ElastiCache), unlike the default docker-compose deployment.

The root cause is that PurlDB uses django-rq, which disables TLS by default unless specific options are passed.

As can be seen in the following lines, only HOST, PORT, PASSWORD, and DEFAULT_TIMEOUT are being set by PurlDB:

purldb/purldb_project/settings.py

Lines 308 to 315 in e638d18

	RQ_QUEUES = {
	"default": {
	"HOST": env.str("PURLDB_REDIS_HOST", default="localhost"),
	"PORT": env.str("PURLDB_REDIS_PORT", default="6379"),
	"PASSWORD": env.str("PURLDB_REDIS_PASSWORD", default=""),
	"DEFAULT_TIMEOUT": env.int("PURLDB_REDIS_DEFAULT_TIMEOUT", default=360),
	}
	}

Without either SSL set to True or URL set to contain rediss:// (two s!), it will not use TLS:
https://github.com/rq/django-rq/blob/cd05d2f427e6bd54ce91f78549f05884fa96753e/django_rq/queues.py#L137

Patches for this have already been added to DejaCode and ScanCode.io:

• https://github.com/aboutcode-org/dejacode/pull/208/files
• https://github.com/aboutcode-org/scancode.io/pull/1467/files

To Reproduce
See above.

Expected behavior
PurlDB should provide an option to enable TLS for the Redis connection in order protect the confidentiality and integrity of the data transmitted between the systems.

Screenshots
Not applicable

Context (OS, Browser, Device, etc.):
Not applicable

[rogu-beta]

This is part of our effort to make DejaCode, ScanCode.io, and PurlDB deployable to Kubernetes in cloud environments like AWS.

Regarding that point I also have a question about the use of --appendonly here:

purldb/docker-compose.common.yml

Line 13 in e638d18

command: redis-server --appendonly yes

Is PurlDB using Redis for any data that must be persisted or simply to enhance availablity? I'm asking because AWS ElastiCache does not offer that option and recommend runnig multi-AZ instead.