Switch splice images to use Canton images

[isegall-da]

Canton now publishes:
canton-base
sequencer
mediator
participant

Canton images are available at:

stable
docker pull
europe-docker.pkg.dev/da-images/public/docker/canton-base:3.4.8
in browser (edited)

unstable
docker pull
europe-docker.pkg.dev/da-images/public-unstable/docker/canton-base:3.5.0-snapshot.20251118.17490.0.vf9530839
in browser (edited)

We should switch to using those in Splice, initially just republishing from Splice.

• initial test (PR, CCI)
• modify the splice Dockerfiles for these four images to be a single line FROM: ....
  • Our scripts should determine the stable vs unstable based on the canton version
  • Remove the splice configs and other content in the image directories