MM-59932: Migrate remaining caches to Redis (#27880)

- We introduce 2 new APIs:
1. Scan: this allows incremental iteration
without blocking the Redis server and is the
recommended way to iterate over keys. With this,
we have entirely removed the need for Keys.
2. RemoveMulti: this allows deletion of multiple
keys in a single operation which optimizes
network round trips.

- While here, we make a small improvement to
GetStatusFromCache, where we remove the shallow
copy which wasn't necessary because we always
serialize the data from the cache.
- We do not use Redis for session cache because of
frequent requests to iterate the entire cache which leads
to a lot of `SCAN` calls.
- Avoid broadcasting status update messages for Redis case.
- Setting cache expiry for status cache
- Removing .Set method altogether to prevent
any chances of setting an item with no expiry.

https://mattermost.atlassian.net/browse/MM-59932

```release-note
NONE
```

server/channels/app/platform/session_test.go

@@ -37,22 +37,35 @@ func TestCache(t *testing.T) {
 	th.Service.sessionCache.SetWithExpiry(session.Token, session, 5*time.Minute)
 	th.Service.sessionCache.SetWithExpiry(session2.Token, session2, 5*time.Minute)
 
-	keys, err := th.Service.sessionCache.Keys()
+	var keys []string
+	err := th.Service.sessionCache.Scan(func(in []string) error {
+		keys = append(keys, in...)
+		return nil
+	})
 	require.NoError(t, err)
 	require.NotEmpty(t, keys)
 
 	th.Service.ClearUserSessionCache(session.UserId)
 
-	rkeys, err := th.Service.sessionCache.Keys()
+	var rkeys []string
+	err = th.Service.sessionCache.Scan(func(in []string) error {
+		rkeys = append(rkeys, in...)
+		return nil
+	})
 	require.NoError(t, err)
 	require.Lenf(t, rkeys, len(keys)-1, "should have one less: %d - %d != 1", len(keys), len(rkeys))
 	require.NotEmpty(t, rkeys)
+	clear(rkeys)
+	rkeys = []string{}
 
 	th.Service.ClearAllUsersSessionCache()
 
-	rkeys, err = th.Service.sessionCache.Keys()
+	err = th.Service.sessionCache.Scan(func(in []string) error {
+		rkeys = append(rkeys, in...)
+		return nil
+	})
 	require.NoError(t, err)
-	require.Empty(t, rkeys)
+	require.Len(t, rkeys, 0)
 }
 
 func TestSetSessionExpireInHours(t *testing.T) {