Use action with input instead of issues as starting point

[astariul]

In order to update the packages on github-hosted pypi, the user is required to open an approriate issue, with the right format.

That's error-prone on the user side.

Instead we should use github-actions with inputs (see https://github.blog/changelog/2021-11-10-github-actions-input-types-for-manual-workflows/).

That will be easier.