fix: caching of assets (correct headers and versioned avatar and variables.css url) (#4118)

* fix: caching of assets (correct headers and versioned avatar url)

* serve variables.css versioned and extend shared max age of assets

* fix TestCommandSide_AddHumanAvatar

* refactor: const types

* refactor: return values

Co-authored-by: Fabi <38692350+hifabienne@users.noreply.github.com>
Co-authored-by: adlerhurst <silvan.reusser@gmail.com>

internal/static/storage.go

@@ -35,3 +35,7 @@ type Asset struct {
 	Location      string
 	ContentType   string
 }
+
+func (a *Asset) VersionedName() string {
+	return a.Name + "?v=" + a.Hash
+}