UDF support

[lunyx]

Is your feature request related to a problem? Please describe.
The list of functions available does not fully encompass what we're trying to achieve with transformations.

Describe the solution you'd like
We'd like the ability to define UDFs (user defined functions) that can transform the data how we want it. This would be used when defining a transformation when creating a new collection. The UDFs should be able to be shared across all collections. Limiting scope to a workspace is optional.

Describe alternatives you've considered
We can work around this by constructing a transformation that uses the existing functions.

Additional context
For something more complex that needs to be shared across multiple collections, it's not easy to manage and maintain. In addition, some of the users constructing these functions are not very technical and it would be useful to have a simplified function that we create that they can use.