Minor change to mssql example

Updated readme with conditional creatino section

Updated examples

Added availability_zone to root module (terraform-aws-modules#40)

Enable db_subnet_group_name variable (terraform-aws-modules#38)

* ✨ Enable db_subnet_group_name variable

If the variable not specify then use the db_subnet_group module

* Disable create_db_subnet_group if db_subnet_group_name is defined

Support conditional creation for the database too. (terraform-aws-mod…

…ules#36)

* Support conditional creation for the database too.

* Database instance outputs need to accommodate the case where count is zero.

* Declare variables that allow conditional creation of the database, parameter group, and subnet group. Pass them from main.tf to the nested modules.

* Consistently accommodate boolean like arguments.

Make name optional (fixes terraform-aws-modules#37)

Add availability zone to instance ressource module (terraform-aws-mod…

…ules#35)

Fix enhanced monitoring policy attachment (terraform-aws-modules#34)

Add create_before_destroy to parameter group (terraform-aws-modules#30)

aws_db_parameter_group (or AWS?) does not support removing previously
defined parameters.

I thought I'd give "taint" a spin and force the parameter group to be
recreated.  terraform tried to delete the parameter group but failed as
it's still in use.

This change allows terraform to migrate the RDS instance to the new
parameter group before destroying the old.