Replace go-migrate with morph (#19116)

db/migrations/postgres/000035_create_sharedchannelattachments.up.sql

@@ -0,0 +1,9 @@
+CREATE TABLE IF NOT EXISTS sharedchannelattachments (
+    id varchar(26) NOT NULL,
+    fileid varchar(26),
+    remoteid varchar(26),
+    createat bigint,
+    lastsyncat bigint,
+    PRIMARY KEY (id),
+    UNIQUE (fileid, remoteid)
+);