refactor: Pass Accept header to requests in contrib.utils.download

[matthewfeickert]

Description

• Resolves Pass Accept header in contrib.utils.download #1491
• First step in addressing Issue Refactor contrib.utils.download internals #1672

The HEPData landing page for the resource file can check if the Accept request HTTP header matches the content type of the resource file and return the content directly if so, for example, curl -LH "Accept: application/x-tar" https://doi.org/10.17182/hepdata.89408.v1/r2.

Checklist Before Requesting Reviewer

• Tests are passing
• "WIP" removed from the title of the pull request
• Selected an Assignee for the PR to be responsible for the log summary

Before Merging

For the PR Assignees:

• Summarize commit messages into a comprehensive review of the PR

* Pass requests the `Accept` HTTP header that matches the content type
of the resource file. The HEPData landing page for the resource
requested can check if the header matches and then return the content
directly.
   - c.f. https://blog.datacite.org/changes-to-doi-content-negotiation/

Co-authored-by: Graeme Watt <Graeme.Watt@durham.ac.uk>

[codecov]

Codecov Report

Merging #1673 (29050d3) into master (fbdce47) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1673   +/-   ##
=======================================
  Coverage   98.05%   98.05%           
=======================================
  Files          64       64           
  Lines        4213     4213           
  Branches      585      585           
=======================================
  Hits         4131     4131           
  Misses         49       49           
  Partials       33       33           

Flag	Coverage Δ
contrib	25.30% <0.00%> (ø)
doctest	61.04% <100.00%> (ø)
unittests	96.36% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/pyhf/contrib/utils.py	100.00% <100.00%> (ø)

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[matthewfeickert]

@GraemeWatt your review here is welcome as well (though I'm lifting your code from Issue #1491).

The pyhf team will address the rest of what's covered in Issue #1672 in follow up PRs.

[GraemeWatt]

Thanks, looks good to me.