### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
randomAlphaOfLength(8),
                null,
                null,
                randomBoolean(),
                new PlainActionFuture<>()
            )
        );
        assertThat(e, instanceOf(FeatureNotEnabledException.class));
        
        assertThat(e, throwableWithMessage("api keys are not enabled"));
        
        assertThat(e.getMetadata(FeatureNotEnabledException.DISABLED_FEATURE_METADATA), contains("api_keys"));
    }
    public void testApiKeyCache() throws IOException {
        final String apiKeyId = randomAlphaOfLength(12);
        final String apiKey = randomAlphaOfLength(16);
        Hasher hasher = getFastStoredHashAlgoForTests();
        final char[] hash = hasher.hash(new SecureString(apiKey.toCharArray()));
        ApiKeyDoc apiKeyDoc = buildApiKeyDoc(hash, -1, false);
        ApiKeyService service = createApiKeyService(Settings.EMPTY);
        ApiKeyCredentials creds = getApiKeyCredentials(apiKeyId, apiKey, apiKeyDoc.type);
        PlainActionFuture<AuthenticationResult<User>> future = new PlainActionFuture<>();
        service.validateApiKeyCredentials(creds.getId(), apiKeyDoc, creds, Clock.systemUTC(), future);
        AuthenticationResult<User> result = future.actionGet();
        assertThat(result.isAuthenticated(), is(true));
        CachedApiKeyHashResult cachedApiKeyHashResult = service.getFromCache(creds.getId());
        assertNotNull(cachedApiKeyHashResult);
        assertThat(cachedApiKeyHashResult.success, is(true));
        creds = getApiKeyCredentials(creds.getId(), "somelongenoughrandomstring", apiKeyDoc.type);
        future = new PlainActionFuture<>();