feat: add setting to prevent implicit workflow creation

[migmartri]

Summary

Add organization-level setting to control whether workflows and projects can be created implicitly during attestation init. This helps prevent workflow and contract sprawl in automated environments.

When prevent_implicit_workflow_creation is enabled, workflows must be created explicitly via chainloop workflow create.

$ go run main.go org update --name testing-123  --prevent-implicit-workflow-creation=true
$ go run main.go att init --workflow sast --project my-project-2222 --release  --replace
ERR creating workflows during the attestation process is disabled for this organization. Please create them in advance or contact your administrator

Changes

• Add prevent_implicit_workflow_creation field to organization
• Add validation in workflow creation to check organization setting
• Add CLI flag --prevent-implicit-workflow-creation to organization update command

Fixes #2526