[Feature] Add `graphman unlink`

Description

Add a command that takes an IPFS hash and removes that deployment from all subgraph names that are using it as their current or pending version. In more detail: if a subgraph uses the hash as its current version, set current_version = pending_version and pending_version = null. If it uses it as the pending version, set pending_version = null.

This command should only accept an IPFS hash, not a subgraph name or sgd identifier.

Currently, this is done with the following pl/pgsql proc which also maintains an auditing table info.deleted_subgraphs; it would be good to keep this auditing, too. The code would have to create the table if it does not exist yet.

create or replace function unlink_deployment(did text)
returns void as
$$
declare
  sg record;
begin
  -- We only handle current and pending versions, even though the code
  -- talks about unuded versions for simplicity. We filter unused versions
  -- out in the queries.
  insert into info.deleted_subgraphs(id, name, sid, version,
                                     deployment, namespace, shard,
                                     subgraph_created_at, version_created_at)
  select ds.id,
         s.name,
         s.id as sid,
         case when v.id = s.current_version then 'current'
              when v.id = s.pending_version then 'pending'
              else 'unused' end as version,
         ds.subgraph as deployment,
         ds.name as namespace,
         ds.shard,
         to_timestamp(s.created_at) as subgraph_created_at,
         to_timestamp(v.created_at) as version_created_at
    from subgraphs.subgraph s,
         deployment_schemas ds,
         subgraphs.subgraph_version v
   where v.subgraph = s.id
     and v.id in (s.current_version, s.pending_version)
     and ds.subgraph = v.deployment
     and v.deployment = did;

  for sg in
    select s.id as sid,
           case when v.id = s.current_version then 'current'
              when v.id = s.pending_version then 'pending'
              else 'unused' end as version,
           case when v.id = s.current_version then 1
              when v.id = s.pending_version then 0
              else 2 end as sort_key
      from subgraphs.subgraph s, subgraphs.subgraph_version v,
           deployment_schemas ds
     where s.id = v.subgraph
       and v.id in (s.current_version, s.pending_version)
       and ds.subgraph = v.deployment
       and v.deployment = did
     order by sort_key
  loop
    if sg.version = 'current' then
      update subgraphs.subgraph
         set current_version = pending_version,
             pending_version = null
       where id = sg.sid;
     elsif sg.version = 'pending' then
      update subgraphs.subgraph
         set pending_version = null
       where id = sg.sid;
     end if;
  end loop;
end;
$$ language plpgsql;

Are you aware of any blockers that must be resolved before implementing this feature? If so, which? Link to any relevant GitHub issues.

No response

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