Allow Science Image Version Hints in Codegen

[BenGalewsky]

As an analyzer I want to be able to lock down my transform to a specific science Image release so I can make my results reproducible

The codegen library returns a science image tag as part of the generated code, but this value is hardcoded in values.yaml

We want the user to be able to provide a version hint and the codegen can decide on a tag and return that

[ponyisi]

This will be done in a codegen-by-codegen way (the way metadata is specified is different for each). The hooks are present already in the ServiceX code, the framework for the codegens themselves is done in ssl-hep/ServiceX_Code_Generator_lib#15 .

In general I recommend that codegens only allow images from vetted sources since otherwise this could be used to execute arbitrary code.

We might also consider adding an endpoint so that valid values of the science image tags can be retrieved by the users, though this might be a bit tricky to do properly.

[ponyisi]

Enabled by #987