### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
service.validateApiKeyCredentials(creds.getId(), apiKeyDoc, creds, Clock.systemUTC(), future);
        result = future.actionGet();
        assertThat(result.isAuthenticated(), is(false));
        final CachedApiKeyHashResult shouldBeSame = service.getFromCache(creds.getId());
        assertNotNull(shouldBeSame);
        assertThat(shouldBeSame, sameInstance(cachedApiKeyHashResult));
        apiKeyDoc = buildApiKeyDoc(hasher.hash(new SecureString("somelongenoughrandomstring".toCharArray())), -1, false);
        creds = getApiKeyCredentials(randomAlphaOfLength(12), "otherlongenoughrandomstring", apiKeyDoc.type);
        future = new PlainActionFuture<>();
        service.validateApiKeyCredentials(creds.getId(), apiKeyDoc, creds, Clock.systemUTC(), future);
        result = future.actionGet();
        assertThat(result.isAuthenticated(), is(false));
        cachedApiKeyHashResult = service.getFromCache(creds.getId());
        assertNotNull(cachedApiKeyHashResult);
        assertThat(cachedApiKeyHashResult.success, is(false));
        creds = getApiKeyCredentials(creds.getId(), "otherlongenoughrandomstring2", apiKeyDoc.type);
        future = new PlainActionFuture<>();
        service.validateApiKeyCredentials(creds.getId(), apiKeyDoc, creds, Clock.systemUTC(), future);
        result = future.actionGet();
        assertThat(result.isAuthenticated(), is(false));
        assertThat(service.getFromCache(creds.getId()), not(sameInstance(cachedApiKeyHashResult)));
        assertThat(service.getFromCache(creds.getId()).success, is(false));
        creds = getApiKeyCredentials(creds.getId(), "somelongenoughrandomstring", apiKeyDoc.type);
        future = new PlainActionFuture<>();
        service.validateApiKeyCredentials(creds.getId(), apiKeyDoc, creds, Clock.systemUTC(), future);
        result = future.actionGet();
        assertThat(result.isAuthenticated(), is(true));
        assertThat(service.getFromCache(creds.getId()), not(sameInstance(cachedApiKeyHashResult)));
        assertThat(service.getFromCache(creds.getId()).success, is(true));
    }