Describe how to do DDL changes for SQL Server

The best practices for creating the capture instance should be discussed, also what happens while it hasn't been created after a column has been updated. Some things to discuss:

• DDL updates while the connector is running vs. doing this in a downtime.
• Multiple DDL updates in close sequence, e.g. a second one before the capture instance has been updated

I.e. I think we should have some systematic discussion of the DDL changes matter in the connectors docs. This also might reveal some remaining loop holes.