cubicweb #3732169 rename command add-source to source-add for consistency [validation pending]

other options are named db-*, schema-*, etc. but options related to source are named add-source and source-sync. renaming to source-add seems better.

prioritynormal
typeenhancement
done in3.19.1
load0.100
load left0.000
closed by#846bc9227394 [serverctl] rename 'add-source' to 'source-add' for consistency's sake (closes #3732169)
patch[serverctl] rename 'add-source' to 'source-add' for consistency's sake (closes #3732169) [applied]