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/platform/services/cache/cache.go

@@ -18,10 +18,6 @@ type Cache interface {
 	// Purge is used to completely clear the cache.
 	Purge() error
 
-	// Set adds the given key and value to the store without an expiry. If the key already exists,
-	// it will overwrite the previous value.
-	Set(key string, value any) error
-
 	// SetWithDefaultExpiry adds the given key and value to the store with the default expiry. If
 	// the key already exists, it will overwrite the previous value
 	SetWithDefaultExpiry(key string, value any) error
@@ -31,16 +27,24 @@ type Cache interface {
 	SetWithExpiry(key string, value any, ttl time.Duration) error
 
 	// Get the content stored in the cache for the given key, and decode it into the value interface.
-	// Return ErrKeyNotFound if the key is missing from the cache
+	// Returns ErrKeyNotFound if the key is missing from the cache
 	Get(key string, value any) error
 
+	// GetMulti returns values for multiple keys in a single operation.
+	// Returns ErrKeyNotFound if the key is missing from the cache.
 	GetMulti(keys []string, values []any) []error
 
 	// Remove deletes the value for a given key.
 	Remove(key string) error
 
-	// Keys returns a slice of the keys in the cache.
-	Keys() ([]string, error)
+	// RemoveMulti deletes multiple keys in a single operation.
+	RemoveMulti(keys []string) error
+
+	// Scan allows incremental iteration over the entire key-space
+	// in a performant manner. It provides a callback that consumers
+	// can use to process the keys. If the callback returns an error,
+	// the scan stops, returning the same error.
+	Scan(f func([]string) error) error
 
 	// GetInvalidateClusterEvent returns the cluster event configured when this cache was created.
 	GetInvalidateClusterEvent() model.ClusterEvent