We add a policy definition for the AllowedSuggestedExitNodes syspolicy setting, allowing admins
to configure a list of exit node IDs to be used as a pool for automatic suggested exit node selection.
We update definitions for policy settings configurable on both a per-user and per-machine basis,
such as UI customizations, to specify class="Both".
Lastly, we update the help text for existing policy definitions to include a link to the KB article
as the last line instead of in the first paragraph.
Updates #12687
Updates tailscale/corp#19681
Signed-off-by: Nick Khyl <nickk@tailscale.com>
788121f475