Add Resource Manager stack resource support

[yashodhanf]

Summary

This PR adds support for managing OCI Resource Manager stacks as a Terraform resource.

Included in this change:

• adds oci_resourcemanager_stack resource support
• preserves ZIP-uploaded Terraform config during read/refresh by calling GetStackTfConfig
• aligns the singular stack data source so ZIP-backed config remains usable there as well
• adds docs and an example for the new resource
• adds acceptance coverage for CRUD and incremental updates
• fixes duplicate database DB system sweeper registration that was blocking the integration test package

Current scope is intentionally limited to ZIP-uploaded stack config.

Validation

Executed successfully:

• go test ./internal/service/resourcemanager/...
• TF_ACC=1 go test ./internal/integrationtest -run TestResourcemanagerStackResource_crud -count=1 -v
• TF_ACC=1 go test ./internal/integrationtest -run TestResourcemanagerStackResource_basic -count=1 -v
• TF_ACC=1 go test ./internal/integrationtest -run TestResourcemanagerStackResource_incrementalUpdates -count=1 -v

Acceptance tests were run with Phoenix profile / security token auth.

Notes

• resource refresh/import reconstructs ZIP config using GetStackTfConfig
• incremental update coverage verifies tag-only, variable-only, and config ZIP-only updates without recreation
• docs and example were added for the new resource workflow

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