Bump docker to version 14.1.0 (PostgreSQL 18.4)

[ihalatci]

What

Cuts the Citus 14.1.0 Docker release. The apt/yum community packages for Citus 14.1 on PostgreSQL 18 already exist and work, but no corresponding Docker image was ever published (the latest published tags are 14/14.0/14.0.0). The citusdata.com download page references citusdata/citus:14.1, which is currently a broken docker run. This bump + the v14.1.0 tag triggers publish_docker_images_on_tag.yml to build and publish 14.1 / 14.1.0 and the -pg17 / -pg16 / -alpine variants.

Changes

• Bump Citus to 14.1.0 across all variants (ARG VERSION, apt pin citus-14.0 → citus-14.1): Dockerfile, postgres-17/, postgres-16/, alpine/Dockerfile.
• Bump the PostgreSQL 18 base to 18.4 (pkgvars postgres_18_version, FROM postgres:18.4, FROM postgres:18.4-alpine) so the published image matches the 18.4 reported by the apt/yum installs. pg17 (17.6) and pg16 (16.10) bases unchanged.
• Bump the alpine source-build toolchain to clang21/llvm21 — the 18.4-alpine base is Alpine 3.24 (built against LLVM 21); the old clang19/llvm19 packages no longer exist there, and the bitcode step requires clang-21.
• docker-compose.yml images → 14.1.0; CHANGELOG.md entry.

Verification (local Docker builds)

Image	Build	Citus	PostgreSQL
latest / PG18 (the :14.1 tag)	OK	14.1.0 (ext 14.1-1)	18.4
alpine (source compile)	OK	14.1.0 (ext 14.1-1)	18.4
pg17	OK (prev. run)	14.1.0	17.6

hll 2.19.citus-1 / topn 2.7.0.citus-1 pins unchanged and install fine.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com