feat: Adds support for disabling Backup Compliance Policy on resource delete

[AgustinBettati]

Description

Link to any related issue(s): CLOUDP-294102 (supporting new delete operation), CLOUDP-293109 (docs clarification)

Tested locally (cloud-dev) that the removal of the resource effectively disabled the Backup Compliance Policy in Atlas UI. In cloud-dev there is no pre-requisite of Disablement Approval. Internal KB has all the details of the process, mentioning how API delete operation fits in.

Type of change:

• Bug fix (non-breaking change which fixes an issue). Please, add the "bug" label to the PR.
• New feature (non-breaking change which adds functionality). Please, add the "enhancement" label to the PR. A migration guide must be created or updated if the new feature will go in a major version.
• Breaking change (fix or feature that would cause existing functionality to not work as expected). Please, add the "breaking change" label to the PR. A migration guide must be created or updated.
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the contributing guides
• I have checked that this change does not generate any credentials and that they are NOT accidentally logged anywhere.
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code
• If changes include deprecations or removals I have added appropriate changelog entries.
• If changes include removal or addition of 3rd party GitHub actions, I updated our internal document. Reach out to the APIx Integration slack channel to get access to the internal document.

Further comments

[github-actions]

APIx bot: a message has been sent to Docs Slack channel

[themantissa]

Small docs change, one question

[themantissa]

Tiny edit to make more clear

Suggested change

-> **IMPORTANT NOTE:** Once a Backup Compliance Policy is enabled, no user, regardless of role, can disable the Backup Compliance Policy via Terraform, or any other method, without contacting MongoDB support. Only once approved for disablement from support, the resource can be removed and the delete operation will successfully disable the Backup Compliance Policy. This means that once enabled some resources defined in Terraform will no longer be modifiable. See the full list of [Backup Compliance Policy Prohibited Actions and Considerations](https://www.mongodb.com/docs/atlas/backup/cloud-backup/backup-compliance-policy/#configure-a-backup-compliance-policy).

-> **IMPORTANT NOTE:** Once a Backup Compliance Policy is enabled, no user, regardless of role, can disable the Backup Compliance Policy via Terraform, or any other method, without contacting MongoDB support. However, if BCP is approved for disablement via the support process, the resource can be removed and the delete operation will successfully disable the Backup Compliance Policy. With Backup Compliance Policy enabled some resources defined in Terraform will no longer be modifiable. See the full list of [Backup Compliance Policy Prohibited Actions and Considerations](https://www.mongodb.com/docs/atlas/backup/cloud-backup/backup-compliance-policy/#configure-a-backup-compliance-policy).

[themantissa]

Question - did we check if the error is clear from the API endpoint if we run delete and it's not marked as deletable? Not quite our purview but we can push back on the creating team if it's not clear (since that could be really confusing for Terraform users if it's not).