Add sampling overhead table and expand/update cutting explanation (backport #342)

[mergify]

This adds a sampling overhead table. I should triple check it. I may push other improvements to the cutting explanation to this branch, too.

EDIT: I've added many other improvements, too.

Fixes #293.
Fixes #373.

---

This is an automatic backport of pull request #342 done by Mergify.

[mergify]

Cherry-pick of 299c849 has failed:

On branch mergify/bp/stable/0.6/pr-342
Your branch is up to date with 'origin/stable/0.6'.

You are currently cherry-picking commit 299c849.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   docs/circuit_cutting/explanation/index.rst
	modified:   releasenotes/notes/0.2/gate-cutting-workflow-ebbedbdb1313b258.yaml

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   test/cutting/qpd/test_qpd.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[coveralls]

Pull Request Test Coverage Report for Build 8728371529

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.541%

---

Totals
Change from base Build 8631862982:	0.0%
Covered Lines:	2346
Relevant Lines:	2508

---

💛 - Coveralls