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/general.go

@@ -0,0 +1,56 @@
+package templates
+
+import (
+	"github.com/chasefleming/elem-go"
+	"github.com/chasefleming/elem-go/attrs"
+	"github.com/chasefleming/elem-go/styles"
+)
+
+var bodyStyle = styles.Props{
+	styles.Margin:     "40px auto",
+	styles.MaxWidth:   "800px",
+	styles.LineHeight: "1.5",
+	styles.FontSize:   "16px",
+	styles.Color:      "#444",
+	styles.Padding:    "0 10px",
+	styles.FontFamily: "Sans-serif",
+}
+
+var headerStyle = styles.Props{
+	styles.LineHeight: "1.2",
+}
+
+func headerOne(text string) *elem.Element {
+	return elem.H1(attrs.Props{attrs.Style: headerStyle.ToInline()}, elem.Text(text))
+}
+
+func headerTwo(text string) *elem.Element {
+	return elem.H2(attrs.Props{attrs.Style: headerStyle.ToInline()}, elem.Text(text))
+}
+
+func headerThree(text string) *elem.Element {
+	return elem.H3(attrs.Props{attrs.Style: headerStyle.ToInline()}, elem.Text(text))
+}
+
+func HtmlStructure(head, body *elem.Element) *elem.Element {
+	return elem.Html(nil,
+		elem.Head(
+			attrs.Props{
+				attrs.Lang: "en",
+			},
+			elem.Meta(attrs.Props{
+				attrs.Charset: "UTF-8",
+			}),
+			elem.Meta(attrs.Props{
+				attrs.HTTPequiv: "X-UA-Compatible",
+				attrs.Content:   "IE=edge",
+			}),
+			elem.Meta(attrs.Props{
+				attrs.Name:    "viewport",
+				attrs.Content: "width=device-width, initial-scale=1.0",
+			}),
+			head,
+		),
+		body,
+	)
+}