fix: Correct random password lifecycle by eagerly creating random password value

[bryantbiggs]

Description

• Correct random password lifecycle by eagerly creating random password value. Instead of linking the random password resource generation to whether or not the instance is a replica in the root, just let the random password eagerly create a value; whether or not the password value generated is used is handled by the db_instance sub-module regardless https://github.com/terraform-aws-modules/terraform-aws-rds/blob/master/modules/db_instance/main.tf#L8

Motivation and Context

• Fix lifecycle dependency issue causing errors when trying to use replicas
• Closes Variable interdependecy casues terraform plan to fail in 4.1.2  #386

Breaking Changes

• No

How Has This Been Tested?

• I have tested and validated these changes using one or more of the provided examples/* projects

[antonbabenko]

This PR is included in version 4.1.3 🎉

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues. If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.