Add link to external SSO profile to profile page

[cpradio]

PR Submitted (ping @nec286)

DEV: Add plugin-outlet to allow SSO sites to put a message on the User Preferences page

@pfaffman, you would use this howto to implement it via a site customization (also see example below)

Using Plugin Outlet Connectors from a Theme or Plugin

Discourse includes hundreds of Plugin Outlets which can be used to inject new content or replace existing contend in the Discourse UI. ‘Outlet arguments’ are made available so that content can be customized based on the context. Choosing an outlet To find the name of a plugin outlet, search Discourse core for “<PluginOutlet”, or use the plugin outlet locations theme component. (e.g. topic-above-posts). Wrapper outlets Some outlets in core look like <PluginOutlet @name="foo" />. These allow …

<script type='text/x-handlebars' data-template-name='/connectors/above-user-preferences/sso_notice'>
{{#if siteSettings.enable_sso}}
  modified contents of connectors/above-user-preferences/sso_notice.hbs file goes here
{{/if}}
</script>