IDP: Bring in relevant docs from other product areas

[jkodroff]

We have a number of pages in the docs that belong under the IDP product:

• Organization Templates are a key feature of Pulumi IDP
• New Project Wizard belongs under IDP since this is how the user consumes organization templates
• The Backstage Plugin, because it is open source, belongs under Pulumi IaC, where it would be grouped with our other open source offerings

Need to investigate the "Deploy with Pulumi" button to figure out where it might go.