Fix / CA Cert Instance Default

[bryantbiggs]

Description

• Update db_instance sub-module to use same default ca_cert_identifier as the root level module default

[vutny]

Thanks for this, @bryantbiggs !

@antonbabenko, please consider to merge it.
From https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/UsingWithRDS.SSL-certificate-rotation.html

The current CA certificates expire on March 5, 2020. Therefore, we strongly recommend completing this change as soon as possible, to avoid disruption on the expiration date. If the change is not completed, your applications will fail to connect to your RDS DB instances using SSL/TLS after March 5, 2020.

[antonbabenko]

Thanks @bryantbiggs !

v2.14.0 has been just released.

[robinbowes]

@antonbabenko Do we need this in the terreform11 branch too?

[github-actions]

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