Bump all QL pack versions to 2.0.0

[jeongsoolee09]

What This PR Contributes

Unify all version of qlpack.yml to 2.0.0. This version number is the tag for the next release.

So far, the versions were all different across qlpacks for each framework and the heuristic-models pack. However, as we plan to do a release, the differences make version numbers fragmented and would make the version lookup a bit tedious (e.g. "which qlpack version correlates to which release tag?"). Therefore, make the versions match the tag versions while bumping it to the next major version in terms of the release tag.

Future Works

• Make a release with version v2.0.0.
• Automate some of the release process:
  1. Automatically bump the version numbers.
  2. Check every night if there is a new CLI release and if so, create a new PR with updated version number in qlt.conf.json.