feat(db): support edge function names in webhook triggers

[JEETDESAI25]

What kind of change does this PR introduce?

Feature

What is the current behavior?

Refs: #1705, supabase/supabase#34139

Webhooks require full URLs, breaking when migrating between environments.

What is the new behavior?

• supabase_functions.http_request() auto-detects slugs vs URLs, reads secrets from vault, injects Authorization header
• Vault secrets synced in start, db push, db reset, migration up/down
• Works for PG14 and PG15+ stacks