[terraform-ibm-event-notifications] Add support to create KMS key in external account

[ocofaigh]

Changes should go into solutions/standard only..

• Add new optional variable ibmcloud_kms_api_key. This should be used in a new provider block like so:

  provider "ibm" {
    alias            = "kms"
    ibmcloud_api_key = var.ibmcloud_kms_api_key != null ? var.ibmcloud_kms_api_key : var.ibmcloud_api_key
    region           = local.kms_region # this value should be parsed from the existing KMS CRN 
  }
  
  provider "ibm" {
    ibmcloud_api_key = var.ibmcloud_api_key
    region           = var.region
  }
  

• The kms module block should use the kms provider alias.

• Support creating cross account s2s auth policy (in KMS account):

  • if value for ibmcloud_kms_api_key is passed, and skip_iam_authorization_policy is set to false, then create a cross account s2s auth policy in the KMS account to allow the exact Event Notification instance GUID reader access to the KMS instance GUID in the KMS account.
  • Ensure that if doing cross account auth policy, the skip_iam_authorization_policy value thats passed to the EN module itself is set to true since we will create the cross account one in the DA itself.

• Review all of the variable descriptions and readme markdowns to ensure its clear that it supports KMS in a different account using the ibmcloud_kms_api_key variable.

[kierramarie]

PR has been merged. Closing issue.