Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/channels/db/migrations/postgres/000016_create_reactions.up.sql

@@ -0,0 +1,31 @@
+CREATE TABLE IF NOT EXISTS reactions(
+    userid VARCHAR(26) NOT NULL,
+    postid VARCHAR(26) NOT NULL,
+    emojiname VARCHAR(64) NOT NULL,
+    createat bigint
+);
+
+ALTER TABLE reactions ADD COLUMN IF NOT EXISTS updateat bigint;
+ALTER TABLE reactions ADD COLUMN IF NOT EXISTS deleteat bigint;
+
+DO $$
+<<alter_pk>>
+DECLARE
+    existing_index text;
+BEGIN
+    SELECT string_agg(a.attname, ',') INTO existing_index
+    FROM pg_constraint AS c
+    CROSS JOIN
+        (SELECT unnest(conkey) FROM pg_constraint WHERE conrelid = 'reactions'::regclass AND contype='p') AS cols(colnum)
+    INNER JOIN pg_attribute AS a ON a.attrelid = c.conrelid AND cols.colnum = a.attnum
+    WHERE c.contype = 'p'
+    AND c.conrelid = 'reactions'::regclass;
+
+    IF COALESCE (existing_index, '') <> text('postid,userid,emojiname') THEN
+        ALTER TABLE reactions
+            DROP CONSTRAINT IF EXISTS reactions_pkey,
+            ADD PRIMARY KEY (postid, userid, emojiname);
+    END IF;
+END alter_pk $$;
+
+ALTER TABLE reactions ADD COLUMN IF NOT EXISTS remoteid VARCHAR(26);