There are a number of ways you could do it, depends on your needs whether it makes sense to implement them:
Use additional Credentials fields: Your script is already using a Credential object to store the API key. You could also store repo information in it with more
Use define template tag steps: If you main concern is making it easier to configure the action, this is useful. Example of doing this is in my Airtable.js Example action.
Store them in a file: You can store a JSON file in iCloud Drive and read it into the script. Not sure what this would gain you, but it’s an option.
If you are just worried about making it easier to configure, you might just add an additional script step that was first in the action and contained just the variable definitions. That makes it easier to direct another user to modify the action for their needs because they know they are save updating just those values.