[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/mysql/000113_create_retentionidsfordeletion_table.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS RetentionIdsForDeletion;

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

@@ -0,0 +1,7 @@
+CREATE TABLE IF NOT EXISTS RetentionIdsForDeletion (
+    Id varchar(26) NOT NULL,
+    TableName varchar(64),
+    Ids json,
+    PRIMARY KEY (Id),
+    KEY idx_retentionidsfordeletion_tablename (TableName)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;