Adding pagination for credential_list and user_credential_list

[tylern4]

This is similar to #738 from the ticket I opened and @derek-globus fixed.

My next goal was to list the collections and found it wasn't paginated so I could only get the first page. I added in similar changes to the other pull request to make these two methods paginated and tested get_collection_list like before.

data = client.paginated.get_collection_list(page_size=1)
for idx, page in enumerate(data.pages()):
    print(f"Page {idx}: {len(page['data'])} item")

Page 0: 1 item
Page 1: 1 item

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📚 Documentation preview 📚: https://globus-sdk-python--739.org.readthedocs.build/en/739/

[derek-globus]

Thanks for the contribution, Nick.

I've double checked the iteration on both of those routes locally & initiated our automated testing.
Assuming that passes without issue, I'll merge this & ensure we get it into v3.20.0