Add new passmanager.replace(index, ...) method

[1ucian0]

Fixed #2179

This PR introduced PassManager.replace() with the same syntax as append (and adds passmanager[index] = pass as sugar). Also extends the drawer to include the index.

[mtreinish]

It looks like this needs a local rebase because the changelog has been removed.

[mtreinish]

From a functional level the code lgtm, but I have a couple of inline comments/questions that I think we should address. Mostly on index vs key and the error message we raise.

[mtreinish]

I was ready to approve this, but then I noticed the release notes were written in markdown, but they need to be rst. We should convert this to rst prior to merging. See: https://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html for an overview of the syntax.

You can build them locally with tox -edocs now (see: https://github.com/Qiskit/qiskit-terra/blob/master/CONTRIBUTING.md#building-release-notes-locally ) or alternatively we build them in CI now. The built output is hosted as an artifact in azure, see: https://dev.azure.com/qiskit-ci/qiskit-terra/_build/results?buildId=3120&view=artifacts for the output from the most recent run on this PR.

[mtreinish]

Also, I do not think the images will work because of how the releases get built in the docs. Reno will parse all the yaml files and build a docutils tree from parsing all the individually listed rst elements in the yaml. The image files never are outside the doc build root so I don't think that they are going to be found via sphinx. There is also the complexity added when we do release the release notes are built via Qiskit/qiskit not the terra repo. Right now it's done manually (which is easy to handle this case), but I've been working on automating that process which will make this much more difficult to handle.

[1ucian0]

It would be great to have support for images, as the visualization module is particularly important for us. Reno seems okey with it (linting passing and creating the report correctly). How do you suggest to solve it for now in this case?

[1ucian0]

I replace the png files with some text that illustrates the images. Let me know if you think looks too obscure...

[mtreinish]

LGTM, thanks for updating the release notes