fix: add property for metadata import from external file

Author: jlahovnik

eodag/api/collection.py

@@ -91,6 +91,11 @@ class Collection(BaseModel):
         repr=False,
     )
 
+    # path to external collection metadata file
+    eodag_stac_collection: Optional[str] = Field(
+        default=None, alias="stacCollection", exclude=True, repr=False
+    )
+
     # Private property to store the eodag internal id value. Not part of the model schema.
     _id: str = PrivateAttr()
     _dag: Optional[EODataAccessGateway] = PrivateAttr(default=None)