### Description

The [Get API key information API](https://www.elastic.co/guide/en/elasticsearch/reference/master/security-api-get-api-key.html) can currently filter the returned keys by:
 * key id/name
 * keys owned by the calling user
 * keys owned by other users, by `realm_name` and `username`

Irrespective of the filtering used, both invalidated and expired (but not yet deleted) keys will be included in the response.
In the response, keys have the `invalidated` boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.

I propose we introduce a way for the API to support retrieving:
* only valid API keys (not return invalidated keys) - using a boolean request parameter
* keys not expired before a certain timestamp - using a timestamp parameter that defaults to "now" - also note that keys' experiation date is always checked against the local node's clock
x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authc/ApiKeyServiceTests.java
assertThat(e.getCause(), instanceOf(IllegalArgumentException.class));
        assertThat(e.getCause().getMessage(), containsString("One of [api key id, api key name, username, realm name] must be specified"));
        String[] realmNames = generateRandomStringArray(4, 4, true, true);
        String username = randomFrom(randomAlphaOfLengthBetween(3, 8), null);
        String apiKeyName = randomFrom(randomAlphaOfLengthBetween(3, 8), null);
        String[] apiKeyIds = generateRandomStringArray(4, 4, true, true);
        if ((realmNames == null || realmNames.length == 0)
            && Strings.hasText(username) == false
            && Strings.hasText(apiKeyName) == false
            && (apiKeyIds == null || apiKeyIds.length == 0)) {
            username = randomAlphaOfLengthBetween(3, 8);
        }
        PlainActionFuture<InvalidateApiKeyResponse> invalidateApiKeyResponseListener = new PlainActionFuture<>();
        service.invalidateApiKeys(realmNames, username, apiKeyName, apiKeyIds, invalidateApiKeyResponseListener);
        final BoolQueryBuilder boolQuery = QueryBuilders.boolQuery().filter(QueryBuilders.termQuery("doc_type", "api_key"));
        if (realmNames != null && realmNames.length > 0) {
            if (realmNames.length == 1) {
                boolQuery.filter(QueryBuilders.termQuery("creator.realm", realmNames[0]));
            } else {
                final BoolQueryBuilder realmsQuery = QueryBuilders.boolQuery();
                for (String realmName : realmNames) {
                    realmsQuery.should(QueryBuilders.termQuery("creator.realm", realmName));
                }
                realmsQuery.minimumShouldMatch(1);
                boolQuery.filter(realmsQuery);
            }
        }
        if (Strings.hasText(username)) {
            boolQuery.filter(QueryBuilders.termQuery("creator.principal", username));
        }