[MM-53291] Data retention improvements (#24253)

* adding new migration for RetentionIdsForDeletion, changing logic for deleting orphaned reactions. Updating delete user and channel endpoints to remove respective reactions

server/channels/db/migrations/postgres/000113_create_retentionidsfordeletion_table.down.sql

@@ -0,0 +1,3 @@
+DROP INDEX IF EXISTS idx_retentionidsfordeletion_tablename;
+
+DROP TABLE IF EXISTS retentionidsfordeletion;

server/channels/db/migrations/postgres/000113_create_retentionidsfordeletion_table.up.sql

@@ -0,0 +1,7 @@
+CREATE TABLE IF NOT EXISTS retentionidsfordeletion (
+    id varchar(26) PRIMARY KEY,
+    tablename varchar(64),
+    ids varchar(26)[]
+);
+
+CREATE INDEX IF NOT EXISTS idx_retentionidsfordeletion_tablename ON retentionidsfordeletion (tablename);