### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
final ApiKey.Type type = parseTypeFromSourceMap(sourceMap);
        final ApiKeyCredentials creds = getApiKeyCredentials(randomAlphaOfLength(12), apiKey, type);
        mockSourceDocument(creds.getId(), sourceMap);
        final ExecutorService mockExecutorService = mock(ExecutorService.class);
        when(threadPool.executor(SECURITY_CRYPTO_THREAD_POOL_NAME)).thenReturn(mockExecutorService);
        Mockito.doAnswer(invocationOnMock -> {
            final AbstractRunnable actionRunnable = (AbstractRunnable) invocationOnMock.getArguments()[0];
            actionRunnable.onRejection(new EsRejectedExecutionException("rejected"));
            return null;
        }).when(mockExecutorService).execute(any(Runnable.class));
        ApiKeyService service = createApiKeyService(Settings.EMPTY);
        final PlainActionFuture<AuthenticationResult<User>> future = new PlainActionFuture<>();
        service.tryAuthenticate(threadPool.getThreadContext(), creds, future);
        final AuthenticationResult<User> authenticationResult = future.get();
        assertEquals(AuthenticationResult.Status.TERMINATE, authenticationResult.getStatus());
        assertThat(authenticationResult.getMessage(), containsString("server is too busy to respond"));
    }
    public void testCreationWillFailIfHashingThreadPoolIsSaturated() {
        final EsRejectedExecutionException rejectedExecutionException = new EsRejectedExecutionException("rejected");
        final ExecutorService mockExecutorService = mock(ExecutorService.class);
        when(threadPool.executor(SECURITY_CRYPTO_THREAD_POOL_NAME)).thenReturn(mockExecutorService);
        Mockito.doAnswer(invocationOnMock -> {
            final AbstractRunnable actionRunnable = (AbstractRunnable) invocationOnMock.getArguments()[0];
            actionRunnable.onRejection(rejectedExecutionException);
            return null;
        }).when(mockExecutorService).execute(any(Runnable.class));
        final Authentication authentication = AuthenticationTestHelper.builder().build();
        final CreateApiKeyRequest createApiKeyRequest = new CreateApiKeyRequest(randomAlphaOfLengthBetween(3, 8), null, null);
        ApiKeyService service = createApiKeyService(Settings.EMPTY);
        final PlainActionFuture<CreateApiKeyResponse> future = new PlainActionFuture<>();