implement custom welcome message (#820)

* implement custom welcome message

This change adds logic for handling custom welcome messages.

* trim welcome message string on POST

Instead of trimming the welcome message every time we are going to send to send
a welcome message, we just trim once when the message is posted from the admin.

config/defaults.go

@@ -4,12 +4,13 @@ import "github.com/owncast/owncast/models"
 
 // Defaults will hold default configuration values.
 type Defaults struct {
-	Name            string
-	Title           string
-	Summary         string
-	Logo            string
-	Tags            []string
-	PageBodyContent string
+	Name                 string
+	Title                string
+	Summary              string
+	ServerWelcomeMessage string
+	Logo                 string
+	Tags                 []string
+	PageBodyContent      string
 
 	DatabaseFilePath string
 	WebServerPort    int
@@ -27,10 +28,11 @@ type Defaults struct {
 // GetDefaults will return default configuration values.
 func GetDefaults() Defaults {
 	return Defaults{
-		Name:    "Owncast",
-		Title:   "My Owncast Server",
-		Summary: "This is brief summary of whom you are or what your stream is. You can edit this description in the admin.",
-		Logo:    "logo.svg",
+		Name:                 "Owncast",
+		Title:                "My Owncast Server",
+		Summary:              "This is brief summary of whom you are or what your stream is. You can edit this description in the admin.",
+		ServerWelcomeMessage: "",
+		Logo:                 "logo.svg",
 		Tags: []string{
 			"owncast",
 			"streaming",