[gpu-op] Adopt semantic version image tags for DCGM Exporter #3201

GPU Operator currently references DCGM Exporter images using the legacy combined tag format:

<dcgm-version>-<exporter-version>-distroless

Upstream now publishes exporter-only semantic version tags, such as 4.9.0.

In this review comment on PR #3163, the DCGM Exporter maintainer recommends switching to X.Y.Z tags and notes that publishing both formats will not continue indefinitely.

Proposed enhancement

Migrate GPU Operator's default DCGM Exporter image references and dependency-update configuration to the upstream semantic version tag format.

For example:

4.7.0-4.9.0-distroless → 4.9.0

Scope

• Update the default image tag in the Helm chart.
• Update the OLM bundle image references, related images, and corresponding digests.
• Update relevant examples and validation fixtures.
• Update Renovate's DCGM Exporter versioning rule, which currently matches the legacy combined format and derives the version from its DCGM prefix.
• Preserve coordinated DCGM/DCGM Exporter updates and verify compatibility using the exporter release's bundled DCGM version.

Acceptance criteria

• Default DCGM Exporter references use a supported X.Y.Z image tag.
• Renovate recognizes and orders updates by the exporter version.
• Helm and OLM references remain consistent, with verified image digests.
• The selected image supports the required architectures and passes the existing image and manifest validation checks.

This is a migration of the default tag format; user-provided image tags should remain supported.