Add progress bar for downloads

[lbm364dl]

I looked at closed issues and there was #22. It seems this was implemented but later removed and is now legacy code. See e.g.

pins-r/R/legacy_pin_download.R

Line 135 in b32da4a

result <- catch_error(httr::GET(path, write_spec, headers, config, http_utils_progress(size = content_length)))

Any comments on what happened with this functionality? There's already a function http_utils_progress(). I created a PR #872 to showcase what I'd like, though take it just as an idea. I'm not sure to what extent you'd like to implement this. I just think progress bars are extremely useful for user interaction. I confess I might be using too large files and pins doesn't encourage that, but long downloads could also just happen because of slow connection, so progress bars are a must for me.