Add hint about possible issues with pgsodium.key and vault.secrets on restoring supabase backup

# Improve documentation ## Link https://zone-www-dot-77vvct6ix-supabase.vercel.app/docs/guides/platform/migrating-within-supabase/backup-restore ## Describe the problem I couldn't restore my project without removing those lines from my data.sql dump. ```sql --- SELECT pg_catalog.setval('"pgsodium"."key_key_id_seq"', 1, false); ``` ```sql --- COPY "vault"."secrets" ("id", "name", "description", "secret", "key_id", "nonce", "created_at", "updated_at") FROM stdin; --- \. ``` ```sql --- COPY "pgsodium"."key" ("id", "status", "created", "expires", "key_type", "key_id", "key_context", "name", "associated_data", "raw_key", "raw_key_nonce", "parent_key", "comment", "user_data") FROM stdin; --- \. ``` For each of these I received permission denied error like `psql:data.sql:5476: ERROR: permission denied for table key` ## Describe the improvement If the permission problem can't be resolved I would find it helpful if the Troubleshooting notes contained further information about possible permission issues when trying to write data to the pgsodium and vault table. My suggestion would be: > if you get "permission denied" errors for sensitive system tables like pgsodium.key or vault.secrets, comment out the related COPY sections in your data.sql file. ## Additional context I followed the steps in the instructions for backup and restore, and also transferred the pgsodium key before running the backup script. These are the exact steps that I followed for the restore process. https://veiled-jewel-7d9.notion.site/Restore-with-Supabase-CLI-1d38ca9dc97980278fccc9fb9c170735?pvs=4