feat: Scope the KMS auth policy to the exact KMS key

[arya-girish-k]

Description

This PR is to update the KMS auth policy so its scope to the exact KMS key.
Git Issue

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Release notes content

This PR is to update the KMS auth policy so its scope to the exact KMS key.

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[arya-girish-k]

/run pipeline

[arya-girish-k]

The Upgrade test fails due to the re-creation of the auth policy, however since we are using create_before_destroy = true there will be no disruption to key access so skipping upgrade test.

[1558](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1559)
    tests.go:186: 
[1559](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1560)
        	Error Trace:	/go/pkg/mod/github.com/terraform-ibm-modules/[email protected]/testhelper/tests.go:186
[1560](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1561)
        	            				/go/pkg/mod/github.com/terraform-ibm-modules/[email protected]/testhelper/tests.go:766
[1561](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1562)
        	            				/__w/terraform-ibm-icd-edb/terraform-ibm-icd-edb/tests/pr_test.go:112
[1562](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1563)
        	Error:      	Should be false
[1563](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1564)
        	Test:       	TestRunUpgradeCompleteExample
[1564](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1565)
        	Messages:   	Resource(s) identified to be destroyed 
[1565](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1566)
        	            	Name: kms_policy
[1566](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1567)
        	            	Address: module.enterprise_db.ibm_iam_authorization_policy.kms_policy[0]
[1567](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1568)
        	            	Actions: [create delete]
[1568](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1569)
        	            	DIFF:
[1569](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1570)
        	            	  Before: 
[1570](https://github.com/terraform-ibm-modules/terraform-ibm-icd-edb/actions/runs/11952416333/job/33318288008#step:7:1571)
        	            		{"id":"cc5c39a6-8ba7-412e-abe0-0dde7b4a15c8","resource_attributes":"SECURE_VALUE_HIDDEN_HASH:-a62e507cc0d98292a5a103fbfde394bf5d6ed3268ed74d55386a4440","source_resource_instance_id":"","source_resource_type":"","source_service_account":"abac0df06b644a9cabc6e44f55b3880e","subject_attributes":"SECURE_VALUE_HIDDEN_HASH:-5c2f31e6cbe717de6fb4a68d8adba64beda457c54c57bede1840ba48","target_resource_group_id":"","target_resource_instance_id":"7504f55e-4fbc-46ca-857c-ebc0feec681c","target_resource_type":"","target_service_name":"kms","transaction_id":"7ad4bcc2dbc64bab849518695edf2810"}```

[arya-girish-k]

/run pipeline

[imprateeksh]

Release notes should be concise and descriptive, without PR-specific details. Please modify to focus on changes done.

[imprateeksh]

To maintain consistency, this can be modified as -

to read the ${local.kms_service} key ${local.kms_key_id} from the instance ${var.existing_kms_instance_guid}"

[arya-girish-k]

As suggested currently paused on working in this issue until the Elastic search PR is completed, as the same changes needs to be integrated into this one.

[arya-girish-k]

@ocofaigh ,As per discussion some more issues will be created related to this issue.And also In order to ensure consistency across our ICD modules / DA should make the same changes as per Elastic search module which is handling by @jor2 .
As of now closing this PR.