Fix git-annex access issues for CLI

[nellh]

This fixes a bug in retrieveKey where the wrong streaming API was used preventing download of keys and improves performance/reliability (especially on Node 19 or later) where storeKey requests would sometimes hang.

One small change to allow tranferKey providers to override headers without losing the authorization header.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a49b7af) 64.89% compared to head (2c41598) 64.89%.

❗ Current head 2c41598 differs from pull request most recent head d90691a. Consider uploading reports for the commit d90691a to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2945   +/-   ##
=======================================
  Coverage   64.89%   64.89%           
=======================================
  Files         378      378           
  Lines       24230    24230           
  Branches      868      868           
=======================================
  Hits        15723    15723           
  Misses       8507     8507           

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