### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
Arrays.asList(ApiKeyService.getOwnersRealmNames(authentication.runAs(AuthenticationTests.randomUser(), lookupRealmRef))),
            containsInAnyOrder(
                lookupRealmRef.getDomain().realms().stream().map(realmIdentifier -> realmIdentifier.getName()).toArray(String[]::new)
            )
        );
        assertThat(
            Arrays.asList(
                ApiKeyService.getOwnersRealmNames(authentication.runAs(AuthenticationTests.randomUser(), lookupRealmRef).token())
            ),
            containsInAnyOrder(
                lookupRealmRef.getDomain().realms().stream().map(realmIdentifier -> realmIdentifier.getName()).toArray(String[]::new)
            )
        );
    }
    public void testAuthWillTerminateIfGetThreadPoolIsSaturated() throws ExecutionException, InterruptedException {
        final String apiKey = randomAlphaOfLength(16);
        final ApiKeyCredentials creds = getApiKeyCredentials(randomAlphaOfLength(12), apiKey, randomFrom(ApiKey.Type.values()));
        SecurityMocks.mockGetRequestException(client, new EsRejectedExecutionException("rejected"));
        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 testAuthWillTerminateIfHashingThreadPoolIsSaturated() throws IOException, ExecutionException, InterruptedException {
        final String apiKey = randomAlphaOfLength(16);
        Hasher hasher = getFastStoredHashAlgoForTests();
        final char[] hash = hasher.hash(new SecureString(apiKey.toCharArray()));
        Map<String, Object> sourceMap = buildApiKeySourceDoc(hash);