Update RStudio imagestream N-1 metadata to reflect Python 3.12 versions

[coderabbitai]

Description

The N-1 blocks in both manifests/base/rstudio-notebook-imagestream.yaml (CPU) and manifests/base/rstudio-gpu-notebook-imagestream.yaml (GPU) have metadata that does not match the placeholders being referenced.

Current State

The N-1 blocks currently declare:

• Python v3.11
• R v4.4
• CUDA 12.6 (GPU variant)
• rstudio-server 2024.12

However, the placeholders reference py312-c9s-2025-2_PLACEHOLDER, indicating these should be Python 3.12 based images.

Required Changes

Update the metadata in the N-1 blocks of both files to reflect the correct software versions for the 2025.2 release with Python 3.12:

• Update Python version from v3.11 to v3.12
• Update R version as appropriate for the 2025.2 release
• Update CUDA version as appropriate for the 2025.2 release (GPU variant)
• Update rstudio-server version as appropriate for the 2025.2 release

Files Affected

• manifests/base/rstudio-notebook-imagestream.yaml
• manifests/base/rstudio-gpu-notebook-imagestream.yaml

Context

This issue was identified during PR review:

• PR: RHAIENG-3206: refactor(manifests/base): replace relative N-k naming convention with absolute version identifiers (e.g. 2025.2) in manifests and env files (ODH part of the work) #2989
• Comment: RHAIENG-3206: refactor(manifests/base): replace relative N-k naming convention with absolute version identifiers (e.g. 2025.2) in manifests and env files (ODH part of the work) #2989 (comment)

cc @jiridanek