Support multiple sources of input files

At that time, input files are either expected on the disk, or fetched through the accompanying peps_download.py script. Other sources shall be supported.

The chosen approach is to use eodag.

Expected subtasks

• Change current fetching method to eodag
• Adapt S1Tiling configuration method
• Document the new configuration
• Document the new dependency
• Introduce the dependency in S1Tiling installation procedures (pip, conda)