Add examples for multi-tenant applications

[AnthonyPhan]

**Is your feature request related to a problem?

All the current example applications are for single tenant applications. This is great for organisations developing in house teams apps, however this will not help independent software vendors (IVFs) to develop solutions that can benefit the wider teams platform and community.

I think it would be a huge missed opportunity for teamsfx not to address this audience as IVFs will create apps that could enrich the teams market place and eco system in the same way a rich app eco system helped IOS and android.

Describe the solution you'd like

• Add example apps for multi-tenant applications.
• Create biceps templates for provisioning multi-tenant applications
• Clearly communicate the implementation differences between single and multi-tenant scenarios
• Clearly communicate the considerations that should be made when building a multi-tenant teams app

Additional context

• We are building a multi-tenant teams application and found many limitations with the current Teamsfx implementation e.g.
• blob storage is no a good hosting choice due to CDN requirement to meet multi-tenant app domain requirements

[ghost]

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