Docs: Update CI documentation for shared runner settings

What does this MR do?

This MR updates the instructions for enabling/disabling the shared runner settings. The button has been replaced with a toggle.

The current documentation can be found here: Enable Shared Runners.

Related issues

This relates to the following issues:

• Use toggle instead of button for enabling/disable shared runners for project settings (Merged)
• [Feature Flag] Rollout of vueify_shared_runners_toggle

The issue pertains to changing the shared runners button into a toggle for better UX.

The feature change is already merged. It is enabled in staging and the project mgandres1/test-ci-project in production. It is currently gated by the vueify_shared_runners_toggle feature flag.

Some screenshots of the feature change being described in the docs:

Before	After

Author's checklist (required)

• Follow the Documentation Guidelines and Style Guide.
• If you have Developer permissions or higher:
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When applicable:

• Update the permissions table.
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• Add/update the feature flag section.

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• Clear typos, like this is a typpo.
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3. Maintainer

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