Rename `gcs.endpoint` to `gcs.service.host`

[Fokko]

To make it in line with Java:

https://github.com/apache/iceberg/blob/6ee6d1327d3811dbd5795c4e87efdc41b7a58eaa/gcp/src/main/java/org/apache/iceberg/gcp/GCPProperties.java#L32

[ndrluis]

@Fokko, I can solve the missing import. Do you mind?

Edit: I discovered that I don't have the permissions to add the commit to your branch.

[Fokko]

Thanks @kevinjqliu, using get_first_property_value is much cleaner