Fix typos in AWS RDS DB instance types (#972)

* Initial plan

* Add missing AWS RDS DB instance types and fix typo

Co-authored-by: wata727 <[email protected]>

* Add comprehensive tests for new instance types

Co-authored-by: wata727 <[email protected]>

* Fix typo in comment: intance -> instance

Co-authored-by: wata727 <[email protected]>

* Revert incorrect instance types, keep only c6gd.metal and typo fixes

Co-authored-by: wata727 <[email protected]>

* Remove db.c6gd.metal, keep only typo fixes

Co-authored-by: wata727 <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: wata727 <[email protected]>

Author: Copilot

rules/aws_db_instance_invalid_type.go

@@ -8,7 +8,7 @@ import (
 	"github.com/terraform-linters/tflint-ruleset-aws/project"
 )
 
-// AwsDBInstanceInvalidTypeRule checks whether "aws_db_instance" has invalid intance type.
+// AwsDBInstanceInvalidTypeRule checks whether "aws_db_instance" has invalid instance type.
 type AwsDBInstanceInvalidTypeRule struct {
 	tflint.DefaultRule
 
@@ -346,7 +346,7 @@ func NewAwsDBInstanceInvalidTypeRule() *AwsDBInstanceInvalidTypeRule {
 			"db.z1d.2xlarge":            true,
 			"db.z1d.xlarge":             true,
 			"db.z1d.large":              true,
-			"db.x2idn.16xlarg":          true,
+			"db.x2idn.16xlarge":         true,
 			"db.x2idn.24xlarge":         true,
 			"db.x2idn.32xlarge":         true,
 			"db.x2iedn.xlarge":          true,