Add templates of some functional algorithms

[jmcarcell]

BEGINRELEASENOTES

• Add examples of a functional Consumer, Producer and Transformer, to be used as templates. The producer is added in place of the previous CreateExampleEventData
• Change the hello world test to use Gaudi::Algorithm, which is not outdated but not recommended in favor of the functional algorithms
• Remove the remaining tests using the outdated GaudiAlg

ENDRELEASENOTES

[jmcarcell]

Maybe not to have an outdated template using GaudiAlg everywhere. More examples would be nice...
And also to be able to update the documentation about writing Gaudi algorithms