IF NOT EXISTS support for CREATE INDEX in SQLite

[Azarattum]

SQLite supports IF NOT EXISTS when creating a new index, however Kysely doesn't give an option to add the modifier. It should look something like:

db.schema
  .createIndex(name)
  .ifNotExists() // Property 'ifNotExists' does not exist on type 'CreateIndexBuilder'.
  .on(table)
  .columns(columns);

[koskimas]

I think all built-in dialects supports this. Let's add it.

[igalklebanov]

PostgreSQL does support it, MySQL doesn't. 🤷