build: modernize Go usage

This commit modernizes Go usage. This was done with:

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

Then files needed to be `go fmt`ed and a few comments needed to be
restored.

The modernizations include replacing

- if/else conditional assignment by a call to the built-in min or max functions added in go1.21
- sort.Slice(x, func(i, j int) bool) { return s[i] < s[j] } by a call to slices.Sort(s), added in go1.21
- interface{} by the 'any' type added in go1.18
- append([]T(nil), s...) by slices.Clone(s) or slices.Concat(s), added in go1.21
- loop around an m[k]=v map update by a call to one of the Collect, Copy, Clone, or Insert functions from the maps package, added in go1.21
- []byte(fmt.Sprintf...) by fmt.Appendf(nil, ...), added in go1.19
- append(s[:i], s[i+1]...) by slices.Delete(s, i, i+1), added in go1.21
- a 3-clause for i := 0; i < n; i++ {} loop by for i := range n {}, added in go1.22

cmd/serve/docker/api.go

@@ -92,7 +92,7 @@ type ErrorResponse struct {
 func newRouter(drv *Driver) http.Handler {
 	r := chi.NewRouter()
 	r.Post(activatePath, func(w http.ResponseWriter, r *http.Request) {
-		res := map[string]interface{}{
+		res := map[string]any{
 			"Implements": []string{"VolumeDriver"},
 		}
 		encodeResponse(w, res, nil, activatePath)
@@ -152,7 +152,7 @@ func newRouter(drv *Driver) http.Handler {
 	return r
 }
 
-func decodeRequest(w http.ResponseWriter, r *http.Request, req interface{}) bool {
+func decodeRequest(w http.ResponseWriter, r *http.Request, req any) bool {
 	if err := json.NewDecoder(r.Body).Decode(req); err != nil {
 		http.Error(w, err.Error(), http.StatusBadRequest)
 		return false
@@ -160,7 +160,7 @@ func decodeRequest(w http.ResponseWriter, r *http.Request, req interface{}) bool
 	return true
 }
 
-func encodeResponse(w http.ResponseWriter, res interface{}, err error, path string) {
+func encodeResponse(w http.ResponseWriter, res any, err error, path string) {
 	w.Header().Set("Content-Type", contentType)
 	if err != nil {
 		fs.Debugf(path, "Request returned error: %v", err)