Revise Sigstore Policy Controller Helm chart details

[jkylekelly]

Why:

GitHub is deprecating its fork of sigstore/policy-controller now that all internal changes are reflected in the upstream package.

Do not merge until github/artifact-attestations-helm-charts#99 has been merged and the new trust-policies helm chart is published.

Closes:

What's being changed (if available, include any code snippets, screenshots, or gifs):

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing and the changes look good in the review environment.

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Pull Request Overview

This PR updates the documentation to reflect GitHub's deprecation of its fork of the Sigstore Policy Controller in favor of the upstream package. The changes transition from GitHub's custom helm charts to the official Sigstore helm charts while maintaining the same functionality.

• Updates policy controller helm chart source from GitHub's fork to upstream Sigstore
• Revises version numbers to match the upstream releases
• Updates trust policies helm chart version

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Table of review links

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The table shows the files in the content directory that were changed in this pull request. This helps you review your changes on a staging server. Changes to the data directory are not included in this table.

Source	Review	Production	What Changed
actions/how-tos/secure-your-work/use-artifact-attestations/enforce-artifact-attestations.md	fpt ghec	fpt ghec

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

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