Support for summaraizer-version: 'latest'

[StefMa]

In #4 (or #14) we use the summaraizer binaries.
There we also introduce the action input summaraizer-version.
This will download the release by the given number.

We also want to support summaraizer-version: 'latest'.
This will use Octokit.getLatestRelease.
According to the docs, getLatestRelease will return the most recent non-prerelease, non-draft release.
Since we don't have such releases (yet), we have to wait until there is one.
Then we can implement it here 🙃