MM-21357: Use typed constant for channel types (#17928)

* MM-21357: Use typed constant for channel types

https://mattermost.atlassian.net/browse/MM-21357

```release-note
- Introduced a new type ChannelType for all channel types.
- Updated the Client4.UpdateChannelPrivacy method to ChannelType.
```

* Address review comments

```release-note
NONE
```

* telemetry fix

```release-note
NONE
```

model/auditconv.go

@@ -60,7 +60,7 @@ func AuditModelTypeConv(val interface{}) (newVal interface{}, converted bool) {
 type auditChannel struct {
 	ID   string
 	Name string
-	Type string
+	Type ChannelType
 }
 
 // newAuditChannel creates a simplified representation of Channel for output to audit log.
@@ -77,7 +77,7 @@ func newAuditChannel(c *Channel) auditChannel {
 func (c auditChannel) MarshalJSONObject(enc *gojay.Encoder) {
 	enc.StringKey("id", c.ID)
 	enc.StringKey("name", c.Name)
-	enc.StringKey("type", c.Type)
+	enc.StringKey("type", string(c.Type))
 }
 
 func (c auditChannel) IsNil() bool {

model/channel.go

@@ -14,11 +14,13 @@ import (
 	"unicode/utf8"
 )
 
+type ChannelType string
+
 const (
-	ChannelTypeOpen    = "O"
-	ChannelTypePrivate = "P"
-	ChannelTypeDirect  = "D"
-	ChannelTypeGroup   = "G"
+	ChannelTypeOpen    ChannelType = "O"
+	ChannelTypePrivate ChannelType = "P"
+	ChannelTypeDirect  ChannelType = "D"
+	ChannelTypeGroup   ChannelType = "G"
 
 	ChannelGroupMaxUsers       = 8
 	ChannelGroupMinUsers       = 3
@@ -40,7 +42,7 @@ type Channel struct {
 	UpdateAt          int64                  `json:"update_at"`
 	DeleteAt          int64                  `json:"delete_at"`
 	TeamId            string                 `json:"team_id"`
-	Type              string                 `json:"type"`
+	Type              ChannelType            `json:"type"`
 	DisplayName       string                 `json:"display_name"`
 	Name              string                 `json:"name"`
 	Header            string                 `json:"header"`

model/client4.go

@@ -2453,8 +2453,8 @@ func (c *Client4) ConvertChannelToPrivate(channelId string) (*Channel, *Response
 }
 
 // UpdateChannelPrivacy updates channel privacy
-func (c *Client4) UpdateChannelPrivacy(channelId string, privacy string) (*Channel, *Response) {
-	requestBody := map[string]string{"privacy": privacy}
+func (c *Client4) UpdateChannelPrivacy(channelId string, privacy ChannelType) (*Channel, *Response) {
+	requestBody := map[string]string{"privacy": string(privacy)}
 	r, err := c.DoApiPut(c.GetChannelRoute(channelId)+"/privacy", MapToJson(requestBody))
 	if err != nil {
 		return nil, BuildErrorResponse(r, err)

model/message_export.go

@@ -11,7 +11,7 @@ type MessageExport struct {
 	ChannelId          *string
 	ChannelName        *string
 	ChannelDisplayName *string
-	ChannelType        *string
+	ChannelType        *ChannelType
 
 	UserId    *string
 	UserEmail *string

model/role.go

@@ -554,7 +554,7 @@ func ChannelModeratedPermissionsChangedByPatch(role *Role, patch *RolePatch) []s
 }
 
 // GetChannelModeratedPermissions returns a map of channel moderated permissions that the role has access to
-func (r *Role) GetChannelModeratedPermissions(channelType string) map[string]bool {
+func (r *Role) GetChannelModeratedPermissions(channelType ChannelType) map[string]bool {
 	moderatedPermissions := make(map[string]bool)
 	for _, permission := range r.Permissions {
 		if _, found := ChannelModeratedPermissionsMap[permission]; !found {

model/role_test.go

@@ -231,7 +231,7 @@ func TestGetChannelModeratedPermissions(t *testing.T) {
 	tests := []struct {
 		Name        string
 		Permissions []string
-		ChannelType string
+		ChannelType ChannelType
 		Expected    map[string]bool
 	}{
 		{

model/shared_channel.go

@@ -16,19 +16,19 @@ import (
 // If "home" is false, then the shared channel is homed remotely, and "RemoteId"
 // field points to the remote cluster connection in "RemoteClusters" table.
 type SharedChannel struct {
-	ChannelId        string `json:"id"`
-	TeamId           string `json:"team_id"`
-	Home             bool   `json:"home"`
-	ReadOnly         bool   `json:"readonly"`
-	ShareName        string `json:"name"`
-	ShareDisplayName string `json:"display_name"`
-	SharePurpose     string `json:"purpose"`
-	ShareHeader      string `json:"header"`
-	CreatorId        string `json:"creator_id"`
-	CreateAt         int64  `json:"create_at"`
-	UpdateAt         int64  `json:"update_at"`
-	RemoteId         string `json:"remote_id,omitempty"` // if not "home"
-	Type             string `db:"-"`
+	ChannelId        string      `json:"id"`
+	TeamId           string      `json:"team_id"`
+	Home             bool        `json:"home"`
+	ReadOnly         bool        `json:"readonly"`
+	ShareName        string      `json:"name"`
+	ShareDisplayName string      `json:"display_name"`
+	SharePurpose     string      `json:"purpose"`
+	ShareHeader      string      `json:"header"`
+	CreatorId        string      `json:"creator_id"`
+	CreateAt         int64       `json:"create_at"`
+	UpdateAt         int64       `json:"update_at"`
+	RemoteId         string      `json:"remote_id,omitempty"` // if not "home"
+	Type             ChannelType `db:"-"`
 }
 
 func (sc *SharedChannel) ToJson() string {