Implement `WITH` for create index

[FuJa0815]

Postgresql and mssql support WITH clauses for CREATE INDEX calls. It would be great for kysely to support these in some way, or at least expose a modifyEnd method for createIndex.

https://www.postgresql.org/docs/current/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS https://learn.microsoft.com/en-us/sql/t-sql/statements/create-index-transact-sql?view=sql-server-ver16#relational_index_option

[igalklebanov]

Hey 👋

It's a niche feature, so I'm leaning towards adding modifyEnd.