Changed all the html into go using go-elem (#2161)

* Changed all the HTML into go using go-elem

            Created templates package in ./hscontrol/templates.
            Moved the registerWebAPITemplate into the templates package as a function to be called.

            Replaced the apple and windows html files with go-elem.

* update flake

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>
Co-authored-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/templates/register_web.go

@@ -0,0 +1,34 @@
+package templates
+
+import (
+	"fmt"
+
+	"github.com/chasefleming/elem-go"
+	"github.com/chasefleming/elem-go/attrs"
+	"github.com/chasefleming/elem-go/styles"
+)
+
+var codeStyleRegisterWebAPI = styles.Props{
+	styles.Display:         "block",
+	styles.Padding:         "20px",
+	styles.Border:          "1px solid #bbb",
+	styles.BackgroundColor: "#eee",
+}
+
+func RegisterWeb(key string) *elem.Element {
+	return HtmlStructure(
+		elem.Title(nil, elem.Text("Registration - Headscale")),
+		elem.Body(attrs.Props{
+			attrs.Style: styles.Props{
+				styles.FontFamily: "sans",
+			}.ToInline(),
+		},
+			elem.H1(nil, elem.Text("headscale")),
+			elem.H2(nil, elem.Text("Machine registration")),
+			elem.P(nil, elem.Text("Run the command below in the headscale server to add this machine to your network: ")),
+			elem.Code(attrs.Props{attrs.Style: codeStyleRegisterWebAPI.ToInline()},
+				elem.Text(fmt.Sprintf("headscale nodes register --user USERNAME --key %s", key)),
+			),
+		),
+	)
+}