fix: define search path in auth functions (supabase#1616)

## What kind of change does this PR introduce?
* Set search_path to empty string in all auth functions

migrations/20240612114525_set_search_path.up.sql

@@ -0,0 +1,43 @@
+-- set the search_path to an empty string to force fully qualified names in the function 
+do $$ 
+begin
+    -- auth.uid() function
+    create or replace function auth.uid() 
+        returns uuid 
+        set search_path to '' 
+    as $func$
+        select nullif(current_setting('request.jwt.claim.sub', true), '')::uuid;
+    $func$ language sql stable;
+
+    -- auth.role() function
+    create or replace function {{ index .Options "Namespace" }}.role() 
+        returns text 
+        set search_path to ''
+    as $func$
+        select nullif(current_setting('request.jwt.claim.role', true), '')::text;
+    $func$ language sql stable;
+
+    -- auth.email() function
+    create or replace function {{ index .Options "Namespace" }}.email() 
+        returns text 
+        set search_path to ''
+    as $func$
+        select 
+        coalesce(
+            current_setting('request.jwt.claim.email', true),
+            (current_setting('request.jwt.claims', true)::jsonb ->> 'email')
+        )::text
+    $func$ language sql stable;
+
+    -- auth.jwt() function
+    create or replace function {{ index .Options "Namespace" }}.jwt()
+        returns jsonb
+        set search_path to ''
+    as $func$
+        select 
+        coalesce(
+            nullif(current_setting('request.jwt.claim', true), ''),
+            nullif(current_setting('request.jwt.claims', true), '')
+        )::jsonb;
+    $func$ language sql stable;
+end $$;