Prometheus: Continued support for created timestamps

This project aims to advance the support for _created lines, or Created Timestamps, in Prometheus. Building on the groundwork laid during GSoC 2023 by @ArthurSens, who introduced this concept, my mentorship will focus on refining the parsing of _created lines from the OpenMetrics (OM) Text format and proposing an optimized solution for their efficient processing. The initial implementation encountered issues with excessive memory usage, so this work will also involve benchmarking and optimizing the OM parser to identify and address potential inefficiencies. Additionally, there is the possibility of calculating or auto-generating created timestamps per scrape job to extend compatibility with OTLP/PRW 2.0.