Follow up to #294 and #281.

@frankharkins found that it works well using the HTML generation script. A key change from Qiskit itself is we have one page per minor release, like release-notes/0.45. We need to make two improvements:

1. Restructure Qiskit/qiskit to have one release note file per release for future releases. Whereas right now they have the file release_notes for all notes from Qiskit 0.45 forward
2. Update our script updateApiDocs.ts to handle new release notes automatically, including the wonkiness of the prior release note files (legacy_release_notes.html).