docs: expandable content feedback from users

[mmcallister]

We've gotten periodic feedback about content being hidden and missed in the expandable sections. Some examples:

the two sections about security best practices and shell completion are hidden in collapsible section, which is not obvious at first. Consider removing the collapsible/detail markdown directive. (/docs/reference/cli/)

Going forward, we shouldn't put content like warnings, best-practices, or similar important details in expandable sections as it could be missed.

what ports and address does the agent need? e.g. how to lock down outbound connections from agents to proxy (/docs/reference/networking/)

For this one, the info is there but it is hidden at first; it’s the only piece on the page presented in a collapsible section.

[mmcallister]

For the first, the content is from includes snippet permission-warning.mdx and is using the html <details> tag, which specifies additional information that the user can open and close on demand. We can use <Details open> instead to keep formatting but not force people to click to see it.

Here are the pages this is used:

admin-guides/access-controls/getting-started.mdx:19:(!docs/pages/includes/permission-warning.mdx!)
admin-guides/api/getting-started.mdx:25:(!docs/pages/includes/permission-warning.mdx!)
admin-guides/management/admin/trustedclusters.mdx:172:(!docs/pages/includes/permission-warning.mdx!)
enroll-resources/application-access/getting-started.mdx:47:(!docs/pages/includes/permission-warning.mdx!)
enroll-resources/kubernetes-access/register-clusters/static-kubeconfig.mdx:15:(!docs/pages/includes/permission-warning.mdx!)
enroll-resources/server-access/getting-started.mdx:45:(!docs/pages/includes/permission-warning.mdx!)
enroll-resources/server-access/guides/recording-proxy-mode.mdx:44:(!docs/pages/includes/permission-warning.mdx!)
enroll-resources/server-access/guides/ssh-pam.mdx:56:(!docs/pages/includes/permission-warning.mdx!)
includes/kubernetes-access/helm/teleport-cluster-prereqs.mdx:6:(!docs/pages/includes/permission-warning.mdx!)
reference/architecture/api-architecture.mdx:29:(!docs/pages/includes/permission-warning.mdx!)
reference/cli/cli.mdx:15:(!docs/pages/includes/permission-warning.mdx!)