Update minor version to 0.8

[github-actions[bot]]

This is an automatic PR triggered by hanneshapke to prepare for 0.7 release.

Approve and merge in order to update main branch to 0.8.

Check out RELEASE.md for more details.

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[github-actions[bot]]

Thanks for the PR! :rocket:

Instructions: Approve using /lgtm and mark for automatic merge by using /merge.