Move seaweed to a dedicated Canonical repo

[MichaelThamm]

The seaweed charm currently lives here:

• https://github.com/sed-i/seaweedfs-k8s-operator

but we should move it to the Canonical org because we actively use its Terraform module in our CI with COS / COS Dev. This includes:

1. Registering the transferred repo with https://github.com/canonical/canonical-repo-automation
2. Moving the Terraform module (currently in -stack) into the new repo