resource/aws_db_instance: Force update when snapshot_identifier is set

[atsushi-ishibashi]

Closes #2859

If there is a reason why update was executed only when password, vpc_security_group_ids, security_group_names were set, please correct me🙇

[radeksimko]

Thanks for the PR, as usually @atsushi-ishibashi

Do you mind attaching an acceptance test with a config that can exercise this new patch?

[atsushi-ishibashi]

@radeksimko Do you have any ideas of an acceptance test for snapshot?
I'm thinking that I make 2 test steps, the first creating db_instance with specifying final_snapshot_identifier and the second restoring db_instance with the snapshot_identifier.
How do you think?

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

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