So I've been creating an automated pipeline and require the ability to change environmental variables in bitbucket pipelines programatically, I have looked at the various pieces of documentation for this and can't make heads or tails of how to actually go about this, I would consider this to be a fairly reasonable use case, I'm not building an application on top of the API, I just want to POST new variables to my pipeline, can you please give me a detailed guide on how to do this, I've been looking through this stuff for days now and have made barely any progress.