New sampling documentation

[amylebar]

Pull request overview

• Replace sampling methodology section with details about the new sampling method
• Minor updates to the natural gas, and propane and fuel oil utility bill sections to make them clearer

Pull Request Author

This pull request makes changes to (select all the apply):

• Documentation
• Infrastructure (includes apptainer image, buildstock batch, dependencies, continuous integration tests)
• Sampling
• Workflow Measures
• Upgrade Measures
• Reporting Measures
• Postprocessing

Author pull request checklist:

• Tagged the pull request with the appropriate label (documentation, infrastructure, sampling, workflow measure, upgrade measure, reporting measure, postprocessing) to help categorize changes in the release notes.
• ComStock documentation updated
• All new and existing tests pass the CI

Review Checklist

This will not be exhaustively relevant to every PR.

• Perform a code review on GitHub
• All related changes have been implemented: data and method additions, changes, tests
• If fixing a defect, verify by running develop branch and reproducing defect, then running PR and reproducing fix
• Reviewed change documentation
• Ensured code files contain License reference
• Results differences are reasonable
• Make sure the newly added measures has been added with tests and indexed properly
• CI status: all tests pass

ComStock Licensing Language - Add to Beginning of Each Code File

# ComStock™, Copyright (c) 2023 Alliance for Sustainable Energy, LLC. All rights reserved.
# See top level LICENSE.txt file for license terms.