Creates or updates a Splunk integration auth token

Creates an HEC API auth token for a Splunk integration if it doesn't exist and updates it otherwise. If the key is updated while the integration is being used by a pipeline, the new key will be picked at pipeline restart, rescaling or an update. Ingestion supports the previous and the updated key for up to 24 hours of a key update. Make sure to change the key used by the agents to send data within 24 hours of an update for a seamless transition