Evaluate Profile-Guided Optimization (PGO)

Hi!

Recently I tested a lot of software with PGO and measured the performance improvements from PGO - the results are [here](https://github.com/zamazan4ik/awesome-pgo/). Since my results show interesting improvements on a lot of databases (including PostgreSQL) I think it would be a good idea to measure PGO effects on Citus as well. If the results will show an improvement - would be great to see a note in the documentation about PGO. Hopefully, it can help with improving Citus performance (at least CPU usage).