### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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
private final Cache<String, ApiKeyService.CachedApiKeyDoc> docCache;
        private final Cache<String, BytesReference> roleDescriptorsBytesCache;
        private final LockingAtomicCounter lockingAtomicCounter;
        ApiKeyDocCache(TimeValue ttl, int maximumWeight) {
            this.docCache = CacheBuilder.<String, ApiKeyService.CachedApiKeyDoc>builder()
                .setMaximumWeight(maximumWeight)
                .setExpireAfterWrite(ttl)
                .build();
            
            
            
            this.roleDescriptorsBytesCache = CacheBuilder.<String, BytesReference>builder()
                .setExpireAfterAccess(TimeValue.timeValueHours(1))
                .setMaximumWeight(maximumWeight * 2L)
                .build();
            this.lockingAtomicCounter = new LockingAtomicCounter();
        }
        public ApiKeyDoc get(String docId) {
            ApiKeyService.CachedApiKeyDoc existing = docCache.get(docId);
            if (existing != null) {
                final BytesReference roleDescriptorsBytes = roleDescriptorsBytesCache.get(existing.roleDescriptorsHash);
                final BytesReference limitedByRoleDescriptorsBytes = roleDescriptorsBytesCache.get(existing.limitedByRoleDescriptorsHash);
                if (roleDescriptorsBytes != null && limitedByRoleDescriptorsBytes != null) {
                    return existing.toApiKeyDoc(roleDescriptorsBytes, limitedByRoleDescriptorsBytes);
                }
            }
            return null;
        }
        public long getInvalidationCount() {
            return lockingAtomicCounter.get();