Update to rspamd 4.x and add configuration options

[stephdl]

Upgrade rspamd to version 4.x using the Alpine edge community repository. Correct the function call in the milter headers configuration. Introduce an option to disable content URLs in rspamd 4.x to maintain previous behavior.

Configuration compatibility review (rspamd 4.0)

Static files (local.d/)

File	Status	Note
options.inc	✅ fixed	include_content_urls = false added
milter_headers.conf	✅ fixed	'add_header' (underscore)
worker-controller.inc	✅ OK	ssl = true not used, no migration needed
classifier-bayes.conf	✅ OK	Single Redis server, no Jump Hash → Ring Hash migration needed
dkim_signing.conf	✅ OK	Standard DKIM config, RFC conformance in 4.x has no impact here
history_redis.conf	✅ OK	{{COMPRESS}} is an internal rspamd substitution, not a template
logging.inc	✅ OK
mx_check.conf	✅ OK
redis.conf	✅ OK

Templates (.j2)

File	Status	Note
actions.conf.j2	✅ OK	Already uses add_header (underscore)
greylist.conf.j2	✅ OK
antivirus.conf.j2	✅ OK
rspamd.conf.local.j2	✅ OK	Settings flow still compatible with symbols_enabled in 4.x
multimap.conf.j2	✅ OK	prefilter/action unchanged in 4.x
rbl.conf.j2	✅ OK	Spamhaus DQS still valid; include_content_urls = false protects URL checks
rbl_group.conf.j2	✅ OK

Infrastructure

File	Status	Note
entrypoint.sh	✅ OK	rspamadm dkim_keygen still valid in 4.x
reload-config	✅ OK	rspamadm template still supported in 4.x
redis-persistent.conf	✅ OK
redis-volatile.conf	✅ OK
unbound.conf	✅ OK

[stephdl]

an upgrade to rspamd4.01 under edge @DavidePrincipi , we could have 3.14 if we go to alpine 3.23 IIRC

[stephdl]

the goal is to go to debian, for glibc target