[DOCS-XXXXX] Add Private Actions Reference

[irving-santiago]

What does this PR do? What is the motivation?

Fixes DOCS-XXXXX

Adds a new "Private Actions Reference" page: runner configuration and field-name crosswalk across host/Helm/Operator installs, the supported actions/integrations matrix, and credential file formats. Also fixes the runner-type ordering in the shared private_actions_allowlist partial to put Agent-based runners before Standalone, per the docs' standing ordering convention.

Merge readiness

• Ready for merge

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AI assistance

Claude Code carried this page's content over from a pre-drafted, QA-verified draft, ran Vale, fixed a stale link to a page moved earlier in this stack, and reworded one column header ("via" → "through") to satisfy the style guide.

Additional notes

Open item carried from planning: whether the supportsExecutionGroups manifest-schema field reaches the build-time workflow_bundles.json data used elsewhere on this page couldn't be verified in this environment (that data is fetched externally at build time).

[irving-santiago]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [DOCS-XXXXX] Add Get Started with Private Actions (Execution Policies quickstart) #39054
• [DOCS-XXXXX] Add Private Actions Reference #39053 👈 (View in Graphite)
• [DOCS-XXXXX] Rewrite Run a Script for Execution Policies #39052
• [DOCS-XXXXX] Add Execution Policies #39051
• [DOCS-XXXXX] Add Authorize Private Actions #39050
• [DOCS-XXXXX] Add Enrollment and Ownership #39049
• [DOCS-XXXXX] Add Set Up a Standalone Private Action Runner #39048
• [DOCS-XXXXX] Rewrite Set Up in the Datadog Agent, add Execution Policies enrollment #39047
• [DOCS-XXXXX] Move Handling Private Action Credentials under Connections #39046
• [DOCS-XXXXX] Rewrite Private Actions Overview for Execution Policies #39045
• Add tracking doc for the Private Actions / Execution Policies stack #39044
• master

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[github-actions]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/irving.santiago/par-ep-09-reference/actions/private_actions/reference