Update extra page content API (#240)

* Mark change stream key api as pre-release

* Add API for changing extra page content. Renanme usercontent -> pagecontent. closes #236

controllers/admin/changePageContent.go

@@ -0,0 +1,35 @@
+package admin
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"github.com/owncast/owncast/config"
+	"github.com/owncast/owncast/controllers"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// ChangeExtraPageContent will change the optional page content
+func ChangeExtraPageContent(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "POST" {
+		controllers.WriteSimpleResponse(w, false, r.Method+" not supported")
+		return
+	}
+
+	decoder := json.NewDecoder(r.Body)
+	var request changeExtraPageContentRequest
+	err := decoder.Decode(&request)
+	if err != nil {
+		log.Errorln(err)
+		controllers.WriteSimpleResponse(w, false, "")
+		return
+	}
+
+	config.Config.InstanceDetails.ExtraPageContent = request.Key
+	controllers.WriteSimpleResponse(w, true, "changed")
+}
+
+type changeExtraPageContentRequest struct {
+	Key string `json:"content"`
+}