### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
);
        PlainActionFuture<AuthenticationResult<User>> future = new PlainActionFuture<>();
        service.loadApiKeyAndValidateCredentials(threadContext, apiKeyCredentials, future);
        final ApiKeyService.CachedApiKeyDoc cachedApiKeyDoc = service.getDocCache().get(docId);
        assertNotNull(cachedApiKeyDoc);
        assertEquals("hulk", cachedApiKeyDoc.creator.get("principal"));
        final BytesReference roleDescriptorsBytes = service.getRoleDescriptorsBytesCache().get(cachedApiKeyDoc.roleDescriptorsHash);
        assertNotNull(roleDescriptorsBytes);
        assertEquals("{}", roleDescriptorsBytes.utf8ToString());
        final BytesReference limitedByRoleDescriptorsBytes = service.getRoleDescriptorsBytesCache()
            .get(cachedApiKeyDoc.limitedByRoleDescriptorsHash);
        assertNotNull(limitedByRoleDescriptorsBytes);
        final List<RoleDescriptor> limitedByRoleDescriptors = service.parseRoleDescriptorsBytes(
            docId,
            limitedByRoleDescriptorsBytes,
            RoleReference.ApiKeyRoleType.LIMITED_BY
        );
        assertEquals(1, limitedByRoleDescriptors.size());
        assertEquals(SUPERUSER_ROLE_DESCRIPTOR, limitedByRoleDescriptors.get(0));
        if (metadata == null) {
            assertNull(cachedApiKeyDoc.metadataFlattened);
        } else {
            assertThat(cachedApiKeyDoc.metadataFlattened, equalTo(XContentTestUtils.convertToXContent(metadata, XContentType.JSON)));
        }
        assertThat(cachedApiKeyDoc.type, is(type));
        
        final String docId2 = randomAlphaOfLength(16);
        final String apiKey2 = randomAlphaOfLength(16);
        ApiKeyCredentials apiKeyCredentials2 = getApiKeyCredentials(docId2, apiKey2, type);
        final Map<String, Object> metadata2 = mockKeyDocument(