Extract script from upload-release-asset workflow

[cka-y]

We can avoid having a scripting code inline by creating a separate script and combining it with upload-release-asset. This keeps the yml file clean and isolated scripts can be tested easier locally.

Originally posted by @davidgamez in https://github.com/MobilityData/gtfs-validator/pull/1529#discussion_r1258709037

Needs #1529 to be merged.

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[davidgamez]

• [ ] Investigate alternatives to upload arbitrary assets to a GitHub release
• [ ] Share with the team and Implement it