EDM4hep <--> LCIO converters

[fdplacido]

BEGINRELEASENOTES

• Implement EDM4hep to LCIO converter on the fly
• Add LCIO to EDM4hep converter on the fly through k4LCIOReader
• Gaudi Tools to be added to Algorithms on demand on options file
• Added testing for EDM4hep -> LCIO conversion and EDM4hep -> LCIO -> EDM4hep conversion, creating the collections artificially, in place.
• Changed testing to get input files from HTTP key4hep
• Added documentation on usage of converters. Updated documentation.

ENDRELEASENOTES

[andresailer]

Adding conversion from LCIO back to EDM4hep

• allow configuring which collections to transform. Can use the Conversion parameter and have 'lcio::...' as the first entry in the field to indicate the conversion is going the other way. Or adding a second parameter, in which case maybe Conversion should be renamed and edm4hep:: or lcio:: wouldn't be needed.
• Storing the output edm4hep collections in the podio/edm4hep file.
• Calls to the k4LCIOReader conversion functionality

[fdplacido]

There is an initial version of the converter back from LCIO to EDM4hep using k4LCIOReader. Note that this PR: key4hep/k4LCIOReader#9 needs to be merged for the converter to be able to access the converter.