Refactor split long functions (#135)

we have big functions that handle all stuff ... we should split this into smaler chuncks so we could test them seperate and make clear cuts in what happens where

Reviewed-on: https://codeberg.org/Codeberg/pages-server/pulls/135

server/handler/hsts.go

@@ -0,0 +1,15 @@
+package handler
+
+import (
+	"strings"
+)
+
+// getHSTSHeader returns a HSTS header with includeSubdomains & preload for MainDomainSuffix and RawDomain, or an empty
+// string for custom domains.
+func getHSTSHeader(host, mainDomainSuffix, rawDomain string) string {
+	if strings.HasSuffix(host, mainDomainSuffix) || strings.EqualFold(host, rawDomain) {
+		return "max-age=63072000; includeSubdomains; preload"
+	} else {
+		return ""
+	}
+}