azd up should display warning message when downloading a non-Azure-Samples template

[puicchan]

This helps to warn customers about potentially downloading malicious repo.

[jongio]

Triage: Deciding this is not a shipblocker.

If we do this, we'll need a way to perm disable.

[savannahostrowski]

After chatting with CELA, we will need to:

• Add a page to our documentation on docs.microsoft.com outlining the risk of running code you didn’t author
• In azd product, show a blurb with link to notice on docs.microsoft.com on azd init
• On GitHub, add a notice to the bottom of our GitHub README

[savannahostrowski]

I believe this can be closed now via #1348