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/windows.go

@@ -0,0 +1,38 @@
+package templates
+
+import (
+	"fmt"
+
+	"github.com/chasefleming/elem-go"
+	"github.com/chasefleming/elem-go/attrs"
+)
+
+func Windows(url string) *elem.Element {
+	return HtmlStructure(
+		elem.Title(nil,
+			elem.Text("headscale - Windows"),
+		),
+		elem.Body(attrs.Props{
+			attrs.Style : bodyStyle.ToInline(),
+		},
+			headerOne("headscale: Windows configuration"),
+			elem.P(nil,
+				elem.Text("Download "),
+				elem.A(attrs.Props{
+					attrs.Href:   "https://tailscale.com/download/windows",
+					attrs.Rel:    "noreferrer noopener",
+					attrs.Target: "_blank"},
+					elem.Text("Tailscale for Windows ")),
+				elem.Text("and install it."),
+			),
+			elem.P(nil,
+				elem.Text("Open a Command Prompt or Powershell and use Tailscale's login command to connect with headscale: "),
+			),
+			elem.Pre(nil,
+				elem.Code(nil,
+					elem.Text(fmt.Sprintf(`tailscale login --login-server %s`, url)),
+				),
+			),
+		),
+	)
+}