Enable functionality to add custom scriban functions.

[coenm]

Is your feature request related to a problem? Please describe.
I want do manipulate some environment variables before using them.

Describe the solution you'd like
I would like to see that per environment, but also in general you can add custom scriban functions.

Describe alternatives you've considered
no

Additional context
empty

[CommonGuy]

Do you want something similar to this? #10

A place where you can define custom scriban functions, which you will call later on?

[coenm]

Yes,
I saw this issue but i thought it was not relevant anymore due to the fact that Scriban added a UUIDv4 variable.