ci: add ggscout workflow template for org-wide adoption

[benjaminrigaud-gg]

Summary

• Adds workflow-templates/ggscout.yml and workflow-templates/ggscout.properties.json
• Makes the ggscout NHI inventory workflow available as a template when any org member clicks Actions > New workflow in any GitGuardian repo
• Users just need to adjust the cron schedule to avoid overlap with other repos

Required secrets (per repo adopting the template)

• DOGFOOD_GITGUARDIAN_API_KEY
• REPO_TOKEN_WITH_SECRET_ACCESS

References

• Linear: NHI-1454
• Source workflow: https://github.com/GitGuardian/ggscout/blob/main/.github/workflows/ggscout.yml
• Reference PR: https://github.com/GitGuardian/satori/pull/3

Test plan

• After merge, go to any org repo > Actions > New workflow
• Verify "ggscout NHI Inventory" appears in the org templates section
• Create a workflow from the template and verify the YAML is correct