* ec2 inventory/rds: (integration tests) migrate to module_defaults and cope with missing security_token
* ec2 inventory/rds: (integration tests) Avoid hard coding the parameter group name
Generated it based on the information returned when creating the RDS instance.
* ec2 inventory/rds: (integration tests) rename templates to .j2 rather than .yml
- avoids throwing yamllint errors
- makes it clear they're templates not the final yaml files.
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