Allow skipSelect blueprints only when one blueprint exists

[callumbwhyte]

Since Umbraco 7.7 it has been possible to configure the behaviour when creating new content via AngularJS – to require the user to select a blueprint / content template, or auto-select one.

If skipSelect is enabled, the first available blueprint is selected. The issue has been if multiple blueprints exist for a specific type the user has no way to select which blueprint to use.

This PR includes an additional check to only skip the content template select dialog if just one option exists – otherwise the user is presented a dialog to select.

[github-actions]

Hi there @callumbwhyte, thank you for this contribution! 👍

While we wait for one of the Core Collaborators team to have a look at your work, we wanted to let you know about that we have a checklist for some of the things we will consider during review:

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[georgebid]

Hey, @callumbwhyte - thanks for the PR! Someone on the team will review this soon 🎁