feat: compile and schema changes for pubsub (#1600)

- adds topics and subscriptions to schema
- extract pubsub declarations from go modules, including which verbs
consume from a subscription
- scaffolds exported topics into `external_module.go`
- this file also now needs to import ftl if there are exported topics as
are included (they call `ftl.RegisterTopic(...)`)
    - `go mod tidy` needs to be called on external modules

Other things of note:

- Topic names must:
- be idents: this allows us to generate external module files with the
variable name as the topic name (with first letter uppercased, so it is
visible to the module)
- start with a lower case letter: this allows us to deterministically
derive the topic name from the generated variable name. (We could remove
this limitation with more work I think, but this was the easiest way I
could derive external topic names)
- Subscription names must be an ident
    - I don't think it'd be too hard to change this one if we want to.

backend/controller/console.go

@@ -143,7 +143,7 @@ func (c *ConsoleService) GetModules(ctx context.Context, req *connect.Request[pb
 					Config: c,
 				})
 
-			case *schema.Database, *schema.Enum, *schema.TypeAlias, *schema.FSM:
+			case *schema.Database, *schema.Enum, *schema.TypeAlias, *schema.FSM, *schema.Topic, *schema.Subscription:
 			}
 		}
 

backend/controller/ingress/alias.go

@@ -65,7 +65,7 @@ func transformAliasedFields(sch *schema.Schema, t schema.Type, obj any, aliaser
 			}
 		case *schema.TypeAlias:
 			return transformAliasedFields(sch, decl.Type, obj, aliaser)
-		case *schema.Config, *schema.Database, *schema.FSM, *schema.Secret, *schema.Verb:
+		case *schema.Config, *schema.Database, *schema.FSM, *schema.Secret, *schema.Verb, *schema.Topic, *schema.Subscription:
 			return fmt.Errorf("%s: unsupported ref type %T", t.Pos, decl)
 		}
 

backend/controller/ingress/ingress.go

@@ -247,7 +247,7 @@ func validateValue(fieldType schema.Type, path path, value any, sch *schema.Sche
 				return fmt.Errorf("%s is not a valid variant of enum %s", inputName, fieldType)
 			}
 
-		case *schema.Config, *schema.Database, *schema.Secret, *schema.Verb, *schema.FSM:
+		case *schema.Config, *schema.Database, *schema.Secret, *schema.Verb, *schema.FSM, *schema.Topic, *schema.Subscription:
 
 		}