### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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/main/java/org/elasticsearch/xpack/security/authc/ApiKeyService.java
builder.field("name", name).field("version", version.id).field("metadata_flattened", metadata);
        addCreator(builder, authentication);
        return builder.endObject();
    }
    
    /**
     * @return `null` if the update is a noop, i.e., if no changes to `currentApiKeyDoc` are required
     */
    @Nullable
    XContentBuilder maybeBuildUpdatedDocument(
        final String apiKeyId,
        final ApiKeyDoc currentApiKeyDoc,
        final Version targetDocVersion,
        final Authentication authentication,
        final BaseUpdateApiKeyRequest request,
        final Set<RoleDescriptor> userRoleDescriptors
    ) throws IOException {
        assert currentApiKeyDoc.type == request.getType();
        if (isNoop(apiKeyId, currentApiKeyDoc, targetDocVersion, authentication, request, userRoleDescriptors)) {
            return null;
        }
        final XContentBuilder builder = XContentFactory.jsonBuilder();
        builder.startObject()
            .field("doc_type", "api_key")
            .field("type", currentApiKeyDoc.type.value())
            .field("creation_time", currentApiKeyDoc.creationTime)
            .field("expiration_time", currentApiKeyDoc.expirationTime == -1 ? null : currentApiKeyDoc.expirationTime)
            .field("api_key_invalidated", false);
        addApiKeyHash(builder, currentApiKeyDoc.hash.toCharArray());
        final List<RoleDescriptor> keyRoles = request.getRoleDescriptors();