Support for additional variable types in Get-SNOWRITMVariableSet

[f0oster]

Is your feature request related to a problem? Please describe.
Some request item variable types, such as multi row variable sets (there are likely others that are similar - I'm not sure), do not appear to store their value within the sc_item_option table, and as such the dotwalked property for the value queried by Get-SNOWRITMVariableSet is empty.

I'm not sure where this data is stored table wise, or what the schema looks like.

Describe the solution you'd like
Update the Get-SNOWRITMVariableSet function to detect the request items variable types, and query any additional tables needed to fetch the values.

With respect to the above, if variable type detection is possible/practical, it might be a good idea to add some constraints on changes made via Set-SNOWRITMVariableSet based on variable types, or to add dynamic update logic based on the type. I'm not sure what would happen if I tried to set a value on a MRVS, but I'm not too keen to test it and find out in case it causes any issues.