Move remaining path functions from Defaults module in cardano-testnet to Cardano.Node.Testnet.Paths in cardano-node

[palas]

Description

Closes #6532.

Move all path and filename definition functions from Testnet.Defaults (in cardano-testnet) to
Cardano.Node.Testnet.Paths (in cardano-node), so that consumers of generated testnet
configurations can reference canonical paths without depending on cardano-testnet.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
  • integration tests
    See Running tests for more details
• Any changes are noted in the CHANGELOG.md for affected package
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-9.6 and ghc-9.12
• Self-reviewed the diff