Explicit repository upload (2nd try)

[Kleidukos]

This PR adds option to specify remote repository.

In case the specified repository is not found in the configuration, or not specified when multiple repositories are configured, a helpful message is displayed to the user:

Error: cabal: Cannot determine a specific hackage repository. Please choose
one with --repository-name. Available repositories are: localhost,
hackage.haskell.org

$ cabal run -- cabal get  -R toto Cabal-syntax
Error: cabal: Cannot find chosen repository toto. Available repositories are:
localhost, hackage.haskell.org

---

Template Α: This PR modifies behaviour or interface

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have not been added, as I don't know how to test upload/get actions in the test monad. Happy to add them if someone shows me how!

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-03-15 12:48 UTC · Rule: squash-merge
• ✅ Checks passed · on draft merge queue: embarking master (26ab5ef) and #11478 together #11620
• ✅ Merged — 2026-03-15 14:30 UTC · at c0bc9c3699001aa1ddf40040c557f79da646f116

This pull request spent 1 hour 42 minutes 11 seconds in the queue, including 1 hour 30 minutes 59 seconds running CI.

Required conditions to merge

• #approved-reviews-by >= 2 [🛡 GitHub branch protection]
  • Explicit repository upload (2nd try) #11478
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  • Explicit repository upload (2nd try) #11478
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  • Explicit repository upload (2nd try) #11478
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[ulysses4ever]

This is certainly significant for the changelog purposes