Refactoring part 1: Fix some annoying linter warnings in API code (#1064)

* names, constants of reusable strings, removed unneeded `if`, replaced deprecated imports

* more deprecated imports replaced

* What is this?))

* Fix a path and quote a var in Dockerfile

* Addressing review comments

---------

Co-authored-by: Konstantin Koval <kkb@ukr.net>

api/utils/media_cache.go

@@ -37,16 +37,16 @@ func CachePathForMedia(albumID int, mediaID int) (string, error) {
 	return photoCachePath, nil
 }
 
-var test_cache_path string = ""
+var testCachePath string = ""
 
-func ConfigureTestCache(tmp_dir string) {
-	test_cache_path = tmp_dir
+func ConfigureTestCache(tmpDir string) {
+	testCachePath = tmpDir
 }
 
 // MediaCachePath returns the path for where the media cache is located on the file system
 func MediaCachePath() string {
-	if test_cache_path != "" {
-		return test_cache_path
+	if testCachePath != "" {
+		return testCachePath
 	}
 
 	photoCache := EnvMediaCachePath.GetValue()

api/utils/utils_test.go

@@ -1,7 +1,6 @@
 package utils_test
 
 import (
-	"io/ioutil"
 	"os"
 	"path"
 	"testing"
@@ -18,7 +17,7 @@ func TestIsDirSymlink(t *testing.T) {
 	test_utils.FilesystemTest(t)
 
 	// Prepare a temporary directory for testing purposes
-	dir, err := ioutil.TempDir("", "testing")
+	dir, err := os.MkdirTemp("", "testing")
 	if err != nil {
 		t.Fatalf("unable to create temp directory for testing")
 	}