### 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boolean property, as well as the `expiration` property that contains the UNIX timestamp past of which the key is no longer valid for authentication.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/core/src/test/java/org/elasticsearch/xpack/core/security/action/apikey/GetApiKeyRequestTests.java
apiKeyName = a[3];
                ownedByAuthenticatedUser = Boolean.parseBoolean(a[4]);
            }
            @Override
            public ActionRequestValidationException validate() {
                return null;
            }
            @Override
            public void writeTo(StreamOutput out) throws IOException {
                super.writeTo(out);
                out.writeOptionalString(realm);
                out.writeOptionalString(user);
                out.writeOptionalString(apiKeyId);
                out.writeOptionalString(apiKeyName);
                out.writeOptionalBoolean(ownedByAuthenticatedUser);
                out.writeBoolean(randomBoolean());
            }
        }
        String[][] inputs = new String[][] {
            { randomNullOrEmptyString(), "user", "api-kid", "api-kname", "false" },
            { "realm", randomNullOrEmptyString(), "api-kid", "api-kname", "false" },
            { "realm", "user", "api-kid", randomNullOrEmptyString(), "false" },
            { randomNullOrEmptyString(), randomNullOrEmptyString(), "api-kid", "api-kname", "false" },
            { "realm", randomNullOrEmptyString(), randomNullOrEmptyString(), randomNullOrEmptyString(), "true" },
            { randomNullOrEmptyString(), "user", randomNullOrEmptyString(), randomNullOrEmptyString(), "true" } };
        String[][] expectedErrorMessages = new String[][] {
            {
                "username or realm name must not be specified when the api key id or api key name is specified",
                "only one of [api key id, api key name] can be specified" },
            {