Parquet ColumnIndex for null columns is written even when statistics are disabled

[etseidl]

Describe the bug
Inspection of the page index metadata shows that the ColumnIndex for columns that are all nulls is written regardless of the setting of GenericColumnWriter::statistics_enabled.

To Reproduce
In the output below, the c_login column has a ColumnIndex entry as well as the expected OffsetIndex. No other columns do.

% target/debug/parquet-rewrite -i parquet-testing/data/delta_byte_array.parquet -o test.parquet --statistics-enabled none
% pqmeta -i test.parquet                                                                                           Rowgroup 0: num_rows:1000
-----------------------------------------------------------

c_customer_id
--------------------------------------------------
OffsetIndex:
  page0: offset:20023 compressed_size:1280 first_row_index:0 var_bytes:16000


c_salutation
--------------------------------------------------
OffsetIndex:
  page0: offset:21404 compressed_size:473 first_row_index:0 var_bytes:3145


c_first_name
--------------------------------------------------
OffsetIndex:
  page0: offset:26992 compressed_size:1325 first_row_index:0 var_bytes:5650


c_last_name
--------------------------------------------------
OffsetIndex:
  page0: offset:35182 compressed_size:1323 first_row_index:0 var_bytes:6011


c_preferred_cust_flag
--------------------------------------------------
OffsetIndex:
  page0: offset:36567 compressed_size:235 first_row_index:0 var_bytes:971


c_birth_country
--------------------------------------------------
OffsetIndex:
  page0: offset:39532 compressed_size:1097 first_row_index:0 var_bytes:8458


c_login
--------------------------------------------------
OffsetIndex:
  page0: offset:40685 compressed_size:26 first_row_index:0 var_bytes:0

ColumnIndex: boundary_order:ASCENDING
  page0: null_page:True min_val: max_val: null_count:1000

c_email_address
--------------------------------------------------
OffsetIndex:
  page0: offset:71199 compressed_size:1334 first_row_index:0 var_bytes:26562


c_last_review_date
--------------------------------------------------
OffsetIndex:
  page0: offset:76368 compressed_size:1200 first_row_index:0 var_bytes:6825

Expected behavior
Null columns should not have a ColumnIndex present when page statistics are not enabled.

Additional context

[alamb]

label_issue.py automatically added labels {'parquet'} from #6011