### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
if (keyRoles != null) {
            logger.trace(() -> format("Building API key doc with updated role descriptors [%s]", keyRoles));
            addRoleDescriptors(builder, keyRoles);
        } else {
            assert currentApiKeyDoc.roleDescriptorsBytes != null;
            builder.rawField("role_descriptors", currentApiKeyDoc.roleDescriptorsBytes.streamInput(), XContentType.JSON);
        }
        addLimitedByRoleDescriptors(builder, userRoleDescriptors);
        builder.field("name", currentApiKeyDoc.name).field("version", targetDocVersion.id);
        assert currentApiKeyDoc.metadataFlattened == null
            || MetadataUtils.containsReservedMetadata(
                XContentHelper.convertToMap(currentApiKeyDoc.metadataFlattened, false, XContentType.JSON).v2()
            ) == false : "API key doc to be updated contains reserved metadata";
        final Map<String, Object> metadata = request.getMetadata();
        if (metadata != null) {
            logger.trace(() -> format("Building API key doc with updated metadata [%s]", metadata));
            builder.field("metadata_flattened", metadata);
        } else {
            builder.rawField(
                "metadata_flattened",
                currentApiKeyDoc.metadataFlattened == null
                    ? ApiKeyDoc.NULL_BYTES.streamInput()
                    : currentApiKeyDoc.metadataFlattened.streamInput(),
                XContentType.JSON
            );
        }
        addCreator(builder, authentication);
        return builder.endObject();
    }
    private boolean isNoop(