Use drop trigger if exists to support pg12

[jingsam]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

create or replace trigger only available up from PG14. When I connect to PG12, migration fails as

storage/migrations/tenant/0026-objects-prefixes.sql

Lines 148 to 169 in 37be2a3

	-- "storage"."prefixes"
	CREATE OR REPLACE TRIGGER "prefixes_delete_hierarchy"
	AFTER DELETE ON "storage"."prefixes"
	FOR EACH ROW
	EXECUTE FUNCTION "storage"."delete_prefix_hierarchy_trigger"();
	-- "storage"."objects"
	CREATE OR REPLACE TRIGGER "objects_insert_create_prefix"
	BEFORE INSERT ON "storage"."objects"
	FOR EACH ROW
	EXECUTE FUNCTION "storage"."objects_insert_prefix_trigger"();
	CREATE OR REPLACE TRIGGER "objects_update_create_prefix"
	BEFORE UPDATE ON "storage"."objects"
	FOR EACH ROW
	WHEN (NEW.name != OLD.name)
	EXECUTE FUNCTION "storage"."objects_insert_prefix_trigger"();
	CREATE OR REPLACE TRIGGER "objects_delete_delete_prefix"
	AFTER DELETE ON "storage"."objects"
	FOR EACH ROW
	EXECUTE FUNCTION "storage"."delete_prefix_hierarchy_trigger"();

storage/migrations/tenant/0035-add-insert-trigger-prefixes.sql

Lines 2 to 8 in 37be2a3

	-- This trigger is used to create the hierarchy of prefixes
	-- When writing directly in the prefixes table
	CREATE OR REPLACE TRIGGER "prefixes_create_hierarchy"
	BEFORE INSERT ON "storage"."prefixes"
	FOR EACH ROW
	WHEN (pg_trigger_depth() < 1)
	EXECUTE FUNCTION "storage"."prefixes_insert_trigger"();

contains unsupported syntax.

What is the new behavior?

Use drop trigger if exists / create trigger instead of create or replace trigger to support pg12.

Additional context

Add any other context or screenshots.