customize-schemas.php is not idempotent

[dpash]

Running customize-schemas.php multiple times results in further modifications of the schemas.

There's three issues:

1. Security information is stripped away, as it doesn't take existing data into account.
2. 'x-expose-headers' is added where as previously it's not included. This seems to be a bug due to it being stripped out when first run.
3. Additions are added multiple times (which results in invalid json due to duplicate parameters in orders.json)

I have fixes for the first two and I'll create a PR for these. I still need to figure out how to resolve the addition issue.

An alternative approach is to download the original schemas to a different directory and then have the customize-schemas.php write out the schemas to new files.

[jlevers]

Hey @dpash -- thanks for the well-thought-out issue.

Totally agree that this is a problem. I've reworked the schema download/customize/generate pipeline in the (still WIP) v6 of the jlevers/selling-partner-api repo to be a) idempotent and b) built using Symfony commands to make it simpler to work on. I'll revisit this repo once that update's done, and make similar updates here.

Appreciate the offer of a PR -- for the sake of simplicity, I'd like to keep the pipeline for this repo as similar as possible to the pipeline in that v6 branch linked above. If you'd be willing to check that out and see if it's easy to wrap your fixes into a similar structure, that would be much appreciated.