feat: Add support for private ca certs

[mrobinson1022]

Added support for private CA acm certificates

Description

Added the following attribute and corresponding variable:

certificate_authority_arn = var.private_authority_arn

variable "private_authority_arn" {
  description = "Private Certificate Authority ARN for issuing private certificates"
  type        = string
  default     = null
}

Motivation and Context

This allows the module to be used for private CA's to issue ACM certificates.

Breaking Changes

There should be no breaking change with this. The variable default is null so not having it declared should not result in any changes.

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects
• I have executed pre-commit run -a on my pull request