Support metadata (for example, for "Multihref advanced")

[dkarlovi]

If you need to create a relation with additional metadata (for example, bill of material would have a relation and a Quantity), you need to be able to specify the relation metadata directly from the interpreter.

The way I see it, this means:

1. being able to specify the mapping of the metadata fields
2. wrapping the relation in the ElementMetadata instance and setting all the mapped metadata on the instance

Maybe some of this is already possible? WDYT?

[dpfaffenbauer]

I am sure it is possible.... But I would create a custom interpreter as it is easier in such cases. But somehow it for sure is possible to make such cases dynamic using values from the importer.

Maybe something like this:

https://wireframe.cc/NBBSk9

[dkarlovi]

A custom interpreter is always an option (I ended up doing that), but IMO the goal should be to cover most of Pimcore's built in options as well as possible, making this solution robust enough to not require custom interpreters in vast majority of cases. This isn't as problematic to implement (on the contrary), the problem is how to map it easily.