### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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/main/java/org/elasticsearch/xpack/security/authc/ApiKeyService.java
Function<SearchHit, T> hitParser,
        ActionListener<Collection<T>> listener
    ) {
        final SecurityIndexManager frozenSecurityIndex = securityIndex.freeze();
        if (frozenSecurityIndex.indexExists() == false) {
            listener.onResponse(Collections.emptyList());
        } else if (frozenSecurityIndex.isAvailable() == false) {
            listener.onFailure(frozenSecurityIndex.getUnavailableReason());
        } else {
            final BoolQueryBuilder boolQuery = QueryBuilders.boolQuery().filter(QueryBuilders.termQuery("doc_type", "api_key"));
            QueryBuilder realmsQuery = filterForRealmNames(realmNames);
            if (realmsQuery != null) {
                boolQuery.filter(realmsQuery);
            }
            if (Strings.hasText(userName)) {
                boolQuery.filter(QueryBuilders.termQuery("creator.principal", userName));
            }
            if (Strings.hasText(apiKeyName) && "*".equals(apiKeyName) == false) {
                if (apiKeyName.endsWith("*")) {
                    boolQuery.filter(QueryBuilders.prefixQuery("name", apiKeyName.substring(0, apiKeyName.length() - 1)));
                } else {
                    boolQuery.filter(QueryBuilders.termQuery("name", apiKeyName));
                }
            }
            if (apiKeyIds != null && apiKeyIds.length > 0) {
                boolQuery.filter(QueryBuilders.idsQuery().addIds(apiKeyIds));
            }
            findApiKeys(boolQuery, filterOutInvalidatedKeys, filterOutExpiredKeys, hitParser, listener);
        }
    }