New plugin: PILAR Plugin

We would like to contribute our filter plugin [PILAR](https://github.com/aaronabraham311/logstash-filter-pilar). This plugin productionizes [PILAR](https://users.encs.concordia.ca/~shang/pubs/ICSE2023_HETONG.pdf), a parameter-insensitive log parser capable of parsing dynamic tokens from a log event (dynamic tokens are tokens in a log event that change often across log events and include user IDs, process IDs, etc.).

Unlike many common parsers like Grok or Dissect, PILAR doesn't require defining common regex patterns. It learns from log data on what parts of a log event is considered static and what is considered dynamic. We hope that a productionized version of PILAR available as a Logstash plugin can encourage developers to use more advanced log parsers directly within the Logstash ecosystem.

Please let us know if there are any questions regarding this plugin submission! Happy to work on them with the relevant Logstash contributor. Thank you in advance!