Allow to have a file as input for ids to download

[ninsbl]

It is possible, that users may want to download a lager number of files by ID.
Therefore, we should consider also the possibility of "file" input to the id option.

[HamedElgizery]

Do you mean by that we can have a TXT file with a list of IDs (separated by commas maybe), and then we could pass that file to the id option, and then download them?

Also, I think it is relevant to mention this here... there is this serialization/deserialization methods provided by eodag, to save the search results as a GeoJSON file. I will add support for that as well.
https://eodag.readthedocs.io/en/stable/notebooks/api_user_guide/5_serialize_deserialize.html

Would it be reasonable to consider other file types... like CSV? Is it typically used in GRASS?

[ninsbl]

A text file with one ID per line would be good.

The EODAG produced GeoJSON makes sense too, but plain text seems more simple, esp. if users identify IDs by other means...

[HamedElgizery]

Added the text file with IDs option here #8

[HamedElgizery]

Merged to trunk. OSGeo#1097