### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
docId,
            apiKeyDoc,
            credentials,
            clock,
            listener.delegateResponse((l, e) -> {
                if (ExceptionsHelper.unwrapCause(e) instanceof EsRejectedExecutionException) {
                    l.onResponse(AuthenticationResult.terminate("server is too busy to respond", e));
                } else {
                    l.onFailure(e);
                }
            })
        );
        final long invalidationCount;
        if (apiKeyDocCache != null) {
            ApiKeyDoc existing = apiKeyDocCache.get(docId);
            if (existing != null) {
                validator.accept(existing);
                return;
            }
            
            invalidationCount = apiKeyDocCache.getInvalidationCount();
        } else {
            invalidationCount = -1;
        }
        final GetRequest getRequest = client.prepareGet(SECURITY_MAIN_ALIAS, docId).setFetchSource(true).request();
        executeAsyncWithOrigin(ctx, SECURITY_ORIGIN, getRequest, ActionListener.<GetResponse>wrap(response -> {
            if (response.isExists()) {
                final ApiKeyDoc apiKeyDoc;
                try (
                    XContentParser parser = XContentHelper.createParser(