[CLD-7046] Ability to disable self hosted server-side requests to CWS (#26070)

* Add 'Disable' config to CloudSettings to prevent the CWS backend from making calls to the Customer Portal

* Add custom error when disabled

* Make Disable setting cloud_restrictable

* Return 422 instead of 400

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Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/cloud.go

@@ -65,10 +65,15 @@ func (api *API) InitCloud() {
 
 func ensureCloudInterface(c *Context, where string) bool {
 	cloud := c.App.Cloud()
+	disabled := c.App.Config().CloudSettings.Disable != nil && *c.App.Config().CloudSettings.Disable
 	if cloud == nil {
 		c.Err = model.NewAppError(where, "api.server.cws.needs_enterprise_edition", nil, "", http.StatusBadRequest)
 		return false
 	}
+	if disabled {
+		c.Err = model.NewAppError(where, "api.server.cws.disabled", nil, "", http.StatusUnprocessableEntity)
+		return false
+	}
 	return true
 }