scp to agentless nodes allowed in spite of RBAC denial

[nklaassen]

Expected behavior:

When ssh_file_copy is set to false in a user's role, they are blocked from using tsh scp for any target node, including agentless nodes.

Current behavior:

tsh scp and OpenSSH scp both work to copy files to/from agentless nodes without error.
The action is correctly denied for teleport nodes.

I'm not sure if it's technically even possible to block file copies, but the test plan indicates the expected behaviour is to block it. So we should either fix this or update the test plan (and docs).

Bug details:

• Teleport version: v13.0.0-alpha.1
• Recreation steps: Create an agentless node. Create a role with ssh_file_copy: false. Assign the role to a user and try tsh scp file user@agentless-node:
• Debug logs