Add multi_thread_greedy_pauli_optimisation

[sjdilkes]

Adds a new transform multi_thread_greedy_pauli_optimisation and pass MultiThreadGreedyPauliSimp that runs GreedyPauliSimp with different seeds in separate threads and returns the smallest circuit.

Related issues

Please mention any github issues addressed by this PR.

Checklist

• I have performed a self-review of my code.
• I have commented hard-to-understand parts of my code.
• I have made corresponding changes to the public API documentation.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the changelog with any user-facing changes.