Migrations 0092_default_workspace_public and 0095_create_singleton_collections assume that there is a default workspace

The migrations 0092 and 0095 assume the existence of a workspace named "System". Such a workspace does not necessarily exist.

0092 should not fail in the absence of a System workspace.

0095 creates two collections in the System workspace. debusine-admin create-workspace creates these collections for every created workspace. The 0095 migration should rather create these collections in every workspace.