Update projects controller to transfer async

What does this MR do and why?

Update projects controller to transfer async

Changes are behind groups_and_projects_async_transfer feature flag

Closes #586547 (closed)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

In rails console:

# 1. Enable the feature flag
Feature.enable(:groups_and_projects_async_transfer)

# 2. Create test data
user = User.find_by(username: "root")

group = Groups::CreateService.new(user, {
  name: "Transfer Target",
  path: "transfer-target",
  organization_id: Organizations::Organization.default_organization.id
}).execute[:group]

project = Projects::CreateService.new(user, {
  name: "Transfer Test",
  path: "transfer-test",
  namespace_id: user.namespace.id,
  organization_id: Organizations::Organization.default_organization.id
}).execute

# 3. Schedule async transfer
service = Projects::TransferService.new(project, user)
result = service.schedule_async_transfer(group)

result                                          # => true
project.project_namespace.reload.state          # => "transfer_scheduled"
service.error                                   # => nil

# 4. Verify worker completed the transfer (wait ~10 seconds)
sleep 10
project.reload
project.full_path                               # => "transfer-target/transfer-test"
project.namespace.full_path                     # => "transfer-target"
project.project_namespace.state                 # => "ancestor_inherited"

# 5. Test failure path
project.project_namespace.update_column(:state, Namespace.states[:creation_in_progress])
service = Projects::TransferService.new(project, user)
result = service.schedule_async_transfer(group)

result                                          # => false
service.error                                   # => "Unable to initiate transfer. The project may already have a transfer in progress."

# Reset state
project.project_namespace.update_column(:state, Namespace.states[:ancestor_inherited])

# 6. Clean up
Project.find_by(path: "transfer-test")&.destroy!
Group.find_by(path: "transfer-target")&.destroy!
Feature.disable(:groups_and_projects_async_transfer)

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