Add support for downloading files with `xoxc` tokens

[isamert]

slack-url-copy-file was not compatible with xoxc tokens which requires cookie to be present with the request. So this MR simply fixes that.

I only tested these changes with an xoxc token, so I'm not sure that it works with other tokens that do not require the cookie but there are no reasons for this to not work.

[jsilve24]

Note, this fixes #558

[Nazar65]

Please merge this PR bcs it's really useful fix :)

[jsilve24]

Please merge

[adamcstephens]

I can confirm this fixes image downloading for me with an xoxc token.

[unhammer]

another happy user, this fixes it for me :grinning:

[Konubinix]

Works for me to. Thank you @isamert