Get client (by ID) API should include Field Filter

[bhatmadhavi]

Describe the problem you'd like to have solved

Current auth0-java SDK does not provide filter option to "get Client By Id" API, which is available in auth0-management API
Please see attachment

This feature is useful if we intend to read only limited client fields.

Describe the ideal solution

Adding new method to ClientsEntity.java, which accepts "FieldsFilter" parameter. This way it won't impact existing get method

public Request<Client> get(String clientId, FieldsFilter filter) {
        Asserts.assertNotNull(clientId, "client id");

        HttpUrl.Builder builder = baseUrl
            .newBuilder()
            .addPathSegments("api/v2/clients")
            .addPathSegment(clientId);
        if (filter != null) {
            for (Map.Entry<String, Object> e : filter.getAsMap().entrySet()) {
                builder.addQueryParameter(e.getKey(), String.valueOf(e.getValue()));
            }
        }
        String url = builder.build().toString();
        CustomRequest<Client> request = new CustomRequest<>(client, url, "GET", new TypeReference<Client>() {
        });
        request.addHeader("Authorization", "Bearer " + apiToken);
        return request;
    }

Alternatives and current work-arounds

Additional information, if any

PR is created to address this #449

[poovamraj]

@bhatmadhavi we have merged the PR you raised - #449

Thanks a lot for your contribution. The changes will be reflected in the next release of the SDK. We will close this issue for now but please feel free to reopen it if you have any more suggestions.