MM-34389: Reliable websockets: First commit (#17297)

* MM-34389: Reliable websockets: First commit

This is the first commit which makes some basic changes
to get it ready for the actual implementation.

Changes include:
- A config field to conditionally enable it.
- Refactoring the WriteMessage along with setting the deadline
to a separate method.

The basic idea is that the client sends the connection_id
and sequence_number either during the handshake (via query params),
or during challenge_auth (via added parameters in the map).

If the conn_id is empty, then we create a new one and set it.
Otherwise, we get the queues from a connection manager (TBD)
and attach them to WebConn.

```release-note
NONE
```

https://mattermost.atlassian.net/browse/MM-34389

* Incorporate review comments

* Trigger CI

* removing telemetry

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/config.go

@@ -373,6 +373,7 @@ type ServiceSettings struct {
 	CollapsedThreads                                  *string `access:"experimental"`
 	ManagedResourcePaths                              *string `access:"environment,write_restrictable,cloud_restrictable"`
 	EnableLegacySidebar                               *bool   `access:"experimental"`
+	EnableReliableWebSockets                          *bool   `access:"experimental"` // telemetry: none
 }
 
 func (s *ServiceSettings) SetDefaults(isUpdate bool) {
@@ -818,6 +819,10 @@ func (s *ServiceSettings) SetDefaults(isUpdate bool) {
 	if s.EnableLegacySidebar == nil {
 		s.EnableLegacySidebar = NewBool(false)
 	}
+
+	if s.EnableReliableWebSockets == nil {
+		s.EnableReliableWebSockets = NewBool(false)
+	}
 }
 
 type ClusterSettings struct {