Provide a way to define primary and secondary XML Indexes

Exposed currently has no way to define xml indexes in MS SQL Server.

E.g:

```
CREATE PRIMARY XML INDEX [primary_xml_index_name] ON [table_name]([xml_column_1])

CREATE XML INDEX secondary_xml_index_name ON [table_name]([xml_column_1]) USING XML INDEX [primary_xml_index_name] FOR VALUE
```

Secondary xml indexes can be on PATH, VALUE, or PROPERTY
Documentation at [XML Indexes](https://learn.microsoft.com/en-us/sql/relational-databases/xml/xml-indexes-sql-server?view=sql-server-ver16)

Note: a probable fix is to allow a listOf < DdlAware > objects to be added ad-hoc to a Table and have run after the table is created. The Index class is defined as a data class which prohibits subclassing.