Add Hamiltonian transform functions for qubit tapering

[soranjh]

Context:
This PR adds functions to transform a Hamiltonian, based on molecular symmetries, such that it acts trivially on a subset of qubits. These qubits can then be removed from the Hamiltonian.

Description of the Change:
The function transform_hamiltonian is added.

Benefits:

Possible Drawbacks:

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
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[codecov]

Codecov Report

Merging #1966 (11878c0) into master (995f04f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1966   +/-   ##
=======================================
  Coverage   99.16%   99.17%           
=======================================
  Files         223      223           
  Lines       17090    17150   +60     
=======================================
+ Hits        16948    17008   +60     
  Misses        142      142           

Impacted Files	Coverage Δ
pennylane/hf/__init__.py	100.00% <ø> (ø)
pennylane/hf/tapering.py	100.00% <100.00%> (ø)

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