2026.b: 🏗️ RHEL 10 (UBI) image support

Build and validate RHEL container images.

Background

First-party Posit product images ship on Ubuntu only today. RHEL/UBI
(registry.access.redhat.com/ubiN/ubi) support has never been attempted
for Connect or Workbench; Package Manager has one in-flight attempt
(images-package-manager#103, not yet merged).

Depends on:

• https://github.com/posit-dev/platform-team/issues/443

Goals

• Standard and Minimal builds of package-manager, connect, and workbench
  on RHEL 10 (UBI), amd64 + arm64
• RHEL 10 support for the connect-content/connect-content-init and
  workbench-session/workbench-session-init matrix and init images
• The images EKS smoke-test pipeline (platform-team#443) validates
  RHEL10/UBI image variants the same way it validates Ubuntu images

External Dependencies and Blockers

• rstudio/r-builds#329 (merged) already fixes the flexiblas-devel hard
  dependency that blocks R on UBI 9/10 — consuming repos just need R
  4.6.1+ to pick it up.
• platform-infra#293 is tracked under the test-automation epic
  (platform-team#443), not natively under this epic.

Notes

Phase 1 (package-manager) in progress: images-package-manager#103,
tracked via images-package-manager#130.