Add RHEL 10 (UBI) support for workbench (Standard/Minimal)

[bschwedler]

Phase 2 of the RHEL 10 (UBI) initiative (posit-dev/images-shared#575).

Workbench has no RHEL/UBI support today — this is first-time enablement.
posit-dev/images-package-manager#130 (RHEL 10 UBI support) is the
closest precedent.

Approach

• Standard and Minimal builds on registry.access.redhat.com/ubi10/ubi,
  amd64 + arm64
• Validate R and Python install and run correctly on RHEL 10 (requires R
  4.6.1+ to avoid the flexiblas-devel issue fixed in
  Allow RHEL RPMs to work on UBI 9/10: make flexiblas-devel a weak dependency rstudio/r-builds#329)

Notes

posit_product/main.py's distro-tag resolver already handles Workbench
generically ("rhel" + version) — no code change needed there.

Don't conflate with workbench-session-init's existing rhel8/rhel9/
rhel10 goss checks — those validate bundled remote-session-launcher
binaries for compute targets, unrelated to this image's own base OS.

Out of scope: workbench-session/workbench-session-init (tracked
separately).