The Active Directory organizational unit for your DB instance to join. Constraints:
Must be in the distinguished name format.
Can't be longer than 64 characters. Example: `OU=mymanagedADtestOU,DC=mymanagedADtest,DC=mymanagedAD,DC=mydomain`
`OU=mymanagedADtestOU,DC=mymanagedADtest,DC=mymanagedAD,DC=mydomain`