Multi-data/layer support

[eblondel]

This ticket is here to reference development tasks related to the multi-layer support:

• [x] Multiple data support for a single entity #263
• [x] Merge 'enrichWithFeatures' / enrichWithCoverages' into single 'enrichWithData' #264
• [x] Enable data enrichment strategies ('first', 'union') for spatial bounding box #265
• [x] Support multi-source 'dir' method for remote accessors (eg. ocs) #304
• [x] Improve 'dir' multi-source approach for geopackage support #324
• [x] Enhance ISO 19110 action for handling common data structure based multi-source features #326