feat(splunk): improve Forge O11y dashboards

[edersonbrilhante]

Description

Improves the Forge Splunk Observability dashboards with additional runner, billing, SQS, and infrastructure impact views.

This change adds a new Forge Impact dashboard and improves the existing EC2 runner, K8S runner, billing, SQS, Lambda, DynamoDB, EBS, and K8S detector coverage. The new and updated charts focus on tenant-level visibility, active runner counts, runner usage over the selected time window, EC2 instance type breakdowns, K8S runner pod counts, runner-minutes, billing impact, and operational signals that help explain Forge adoption and troubleshooting impact.

The runner impact charts were refined to avoid counting unrelated resources:

• EC2 runner totals and runner-minutes now require aws_tag_TenantName where tenant attribution is needed.
• K8S runner totals use the runner container memory metric as a pod presence signal instead of readiness or CPU time metrics that were inaccurate for this use case.
• The Forge Impact dashboard is placed in the shared Splunk O11y dashboard group used by the rest of the Forge dashboards.

Type of Change

• Bug Fix
• New Feature
• Breaking Change
• Refactor
• Documentation
• Other (please describe)

Checklist

• I have read the contributing guidelines
• Existing issues have been referenced (where applicable)
• I have verified this change is not present in other open pull requests
• Functionality is documented
• All code style checks pass
• New code contribution is covered by automated tests
• All new and existing tests pass

Validation

• Terraform/Tofu format and validate passed through the repository commit hooks.
• Gitleaks and static pre-commit checks passed through the repository commit hooks.
• Verified no existing open PR for branch improve-splunk-o11y-dashboards before creating this PR.