Add handling nested properties during resolving jwt placeholders

[dimabarbul]

Resolves #1985

[thjaeckle]

@dimabarbul thanks a lot for the PR. Will review next week once back from my vacation.

[dimabarbul]

@thjaeckle Give me some time (couple of days or so), please, I want to make another version with HashSet instead of Stream for comparison. I haven't checked performance, but I'm pretty sure, HashSet version should be better.

[dimabarbul]

HashSet version is:

    private static Set<String> resolveValues(final JsonValue jsonValue, final JsonPointer jsonPointer) {
        final Set<String> result = new HashSet<>();

        resolveValuesInner(jsonValue, jsonPointer, result);

        return result;
    }

    private static void resolveValuesInner(
            final JsonValue jsonValue, final JsonPointer jsonPointer, final Set<String> result) {
        jsonPointer.getRoot()
                .ifPresentOrElse(
                        root -> {
                            if (jsonValue.isArray()) {
                                jsonValue.asArray().stream()
                                        .forEach(item -> resolveValuesInner(item, jsonPointer, result));
                            } else if (jsonValue.isObject()) {
                                jsonValue.asObject().getValue(root)
                                        .ifPresent(v -> resolveValuesInner(v, jsonPointer.nextLevel(), result));
                            }
                        },
                        () -> {
                            if (jsonValue.isArray()) {
                                jsonValue.asArray().stream().map(JsonValue::formatAsString).forEach(result::add);
                            } else {
                                result.add(jsonValue.formatAsString());
                            }
                        });
    }

I've roughly measured performance of HashSet and Stream versions (using System.currentTimeMillis) and found that time is relatively the same (with stream version slightly better). So I'll leave the PR as is.