Give users an option to filter visible options (current) or allow them to Search their Azure Tenant via feature flag

[cricketthomas]

This feature previously existed (v2.0.0.2) but was removed when reverting to more stable filtering of visible items.

https://github.com/cricketthomas/AzureKeyVaultExplorer/blob/52dbfc4c4a140d4024b71258170d062c34e262a0/src/uno/AzureKeyVaultStudio/AzureKeyVaultStudio/Services/AzureSearchService.cs