New Snippet example for Shared Image Gallery

[fberson]

Adding new Code Snippet for Shared Image Gallery Resource.

Contributing a snippet

• I have only a single resource in my snippet
• I have checked that there is not an equivalent snippet already submitted
• I have used camelCasing unless I have a justification to use another casing style
• I have placeholders values that correspond to their property names (e.g. dnsPrefix: 'dnsPrefix'), unless it's a property that MUST be changed or parameterized in order to deploy. In that case, I use 'REQUIRED' e.g. keyData
• I have my symbolic name as the first tab stop ($1) in the snippet. e.g. res-aks-cluster.bicep
• I have a resource name property equal to "name"

[MarcusFelling]

@fberson - thank you for another contribution! I will review once #2307 is completed.

[MarcusFelling]

Thanks for your patience on this @fberson. The new standards have been merged. Please see requested changes below.