Support FIRST and AFTER clause when adding a new column in engine and Iceberg connector

[ebyhr]

Description

This needs syntax review as the corresponding rule doesn't exist in SQL standard.

Datasources supporting these options:

• Spark https://iceberg.apache.org/docs/latest/spark-ddl/#alter-table-add-column
• Hive https://cwiki.apache.org/confluence/display/hive/languagemanual+ddl
• MySQL https://dev.mysql.com/doc/refman/8.3/en/alter-table.html
• ClickHouse https://clickhouse.com/docs/en/sql-reference/statements/alter/column#add-column

Fixes #20091

Release notes

(x) Release notes are required, with the following suggested text:

# General, Iceberg
* Add support `FIRST` and `AFTER` clause when adding a new column. ({issue}`20091`)

[findinpath]

From a Zoom Meeting with @martint , @electrum

Support adding a field with ADD COLUMN in Iceberg
#16321

It would be nice to support adding nested fields in ROW types.

Positioning of the fields seems also attractive (FIRST/ AFTER column), but it is not in the spec.
Reference https://iceberg.apache.org/docs/latest/spark-ddl/
Alternative scenario in Trino for specifying the exact position of the new nested field in the row: ALTER COLUMN ... SET DATA TYPE

FIRST/AFTER - let’’s wait for request from the community to actually start any work on this area.