Allow inline JSON in config.json for advanced logging config (#20954)

* Allow embedded JSON in config.json for AdvancedLoggingConfig

* fix escaped JSON case

* Add unit test cases for escaped JSON

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

config/utils_test.go

@@ -276,7 +276,7 @@ func TestIsJSONMap(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if got := isJSONMap(tt.data); got != tt.want {
+			if got := isJSONMap([]byte(tt.data)); got != tt.want {
 				t.Errorf("isJSONMap() = %v, want %v", got, tt.want)
 			}
 		})