Automatically Trigger Expired Token Removal

[slobodanadamovic]

Description

Elasticsearch supports removal of expired tokens (created >24h). It provides a configurable interval at which the expired token remover should scan for expired tokens and delete them. The interval is controlled via xpack.security.authc.token.delete.interval setting. This setting is undocumented but we should fix that.

Currently, the removal of expired tokens is only triggered when a manual call to the Invalidate Token API is made. This behaviour is unexpected and can lead to indefinite grow of .security-tokens index.

We should improve the expired token remover to be triggered automatically (per defined interval), instead of requiring a call to the invalidate token API.

[elasticsearchmachine]

Pinging @elastic/es-security (Team:Security)