Fixup request-tls for remote loading of manifests

[jhugman]

This PR fixes an issue with fetching of remote files via reqwest and tls.

It also introduces a fetch command to the nimbus-fml command line.

Pull Request checklist

• Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry in CHANGES_UNRELEASED.md or an explanation of why it does not need one
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  • Any new dependencies are accompanied by a summary of the due dilligence applied in selecting them.

Branch builds: add [ac: android-components-branch-name] and/or [fenix: fenix-branch-name] to the PR title.

[codecov-commenter]

Codecov Report

Merging #5047 (005287a) into main (8ae6b57) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #5047   +/-   ##
=======================================
  Coverage   38.49%   38.49%           
=======================================
  Files         168      168           
  Lines       12382    12382           
=======================================
  Hits         4766     4766           
  Misses       7616     7616           

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