REST: Set fresh IDs on create-table (#327)

For the other implementation we do this when writing
the metadata, but for the REST catalog we just post
the schema itself.

The REST spec does not mention anything about
setting fresh IDs, so it is best to do it ourselves.

pyiceberg/catalog/rest.py

@@ -58,7 +58,7 @@
     UnauthorizedError,
 )
 from pyiceberg.partitioning import UNPARTITIONED_PARTITION_SPEC, PartitionSpec
-from pyiceberg.schema import Schema
+from pyiceberg.schema import Schema, assign_fresh_schema_ids
 from pyiceberg.table import (
     CommitTableRequest,
     CommitTableResponse,
@@ -447,13 +447,14 @@ def create_table(
         sort_order: SortOrder = UNSORTED_SORT_ORDER,
         properties: Properties = EMPTY_DICT,
     ) -> Table:
-        schema: Schema = self._convert_schema_if_needed(schema)  # type: ignore
+        iceberg_schema = self._convert_schema_if_needed(schema)
+        iceberg_schema = assign_fresh_schema_ids(iceberg_schema)
 
         namespace_and_table = self._split_identifier_for_path(identifier)
         request = CreateTableRequest(
             name=namespace_and_table["table"],
             location=location,
-            table_schema=schema,
+            table_schema=iceberg_schema,
             partition_spec=partition_spec,
             write_order=sort_order,
             properties=properties,