Outbound live stream notifications (#1663)

* First pass at browser, discord, twilio notifications

* Commit updated Javascript packages

* Remove twilio notification support

* Email notifications/smtp support

* Fix Firefox notification support, remove chrome checks

* WIP more email work

* Add support for twitter notifications

* Add stream title to discord and twitter notifications

* Update notification registration modal

* Fix hide/show email section

* Commit updated API documentation

* Commit updated Javascript packages

* Fix post-rebase missing var

* Remove unused var

* Handle unsubscribe errors for browser push

* Standardize email config prop names

* Allow overriding go live email template

* Some notifications cleanup

* Commit updated Javascript packages

* Remove email/smtp/mailjet support

* Remove more references to email notifications

Co-authored-by: Owncast <owncast@owncast.online>

notifications/discord/discord.go

@@ -0,0 +1,61 @@
+package discord
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+
+	"github.com/pkg/errors"
+)
+
+// Discord is an instance of the Discord service.
+type Discord struct {
+	name       string
+	avatar     string
+	webhookURL string
+}
+
+// New will create a new instance of the Discord service.
+func New(name, avatar, webhook string) (*Discord, error) {
+	return &Discord{
+		name:       name,
+		avatar:     avatar,
+		webhookURL: webhook,
+	}, nil
+}
+
+// Send will send a message to a Discord channel via a webhook.
+func (t *Discord) Send(content string) error {
+	type message struct {
+		Username string `json:"username"`
+		Content  string `json:"content"`
+		Avatar   string `json:"avatar_url"`
+	}
+
+	msg := message{
+		Username: t.name,
+		Content:  content,
+		Avatar:   t.avatar,
+	}
+
+	jsonText, err := json.Marshal(msg)
+	if err != nil {
+		return errors.Wrap(err, "error marshalling discord message to json")
+	}
+
+	req, err := http.NewRequest("POST", t.webhookURL, bytes.NewReader(jsonText))
+	if err != nil {
+		return errors.Wrap(err, "error creating discord webhook request")
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+
+	client := &http.Client{}
+
+	resp, err := client.Do(req)
+	if err != nil {
+		return errors.Wrap(err, "error executing discord webhook")
+	}
+
+	return resp.Body.Close()
+}