Add Imp tests to cover more cases of active/inactive committee

[carlostome]

Description

• Move test "Committee proposals pass" to its proper place
• Add tests covering the following cases:
  • When CC threshold is 0:
    1. Non expired committee without hot credentials
    2. Active committee not voting
    3. Active committee voting whatever
    4. Min committee size = 0
  • When CC threshold is not 0:
    1. Min committee size = 0

Related to #5418

Checklist

• Commits in meaningful sequence and with useful messages.
• Tests added or updated when needed.
• CHANGELOG.md files updated for packages with externally visible changes.
  NOTE: New section is never added with the code changes. (See RELEASING.md).
• Versions updated in .cabal and CHANGELOG.md files when necessary, according to the
  versioning process.
• Version bounds in .cabal files updated when necessary.
  NOTE: If bounds change in a cabal file, that package itself must have a version increase. (See RELEASING.md).
• Code formatted (use scripts/fourmolize.sh).
• Cabal files formatted (use scripts/cabal-format.sh).
• CDDL files are up to date (use scripts/gen-cddl.sh)
• hie.yaml updated (use scripts/gen-hie.sh).
• Self-reviewed the diff.