Automatic PR to master in the release process

[r4mmer]

Motivation

During the release process, changes made on the release-candidate and release branches should be merged back into master.
This is meant to create a common history in the git DAG and prevent conflicts between these branches.

This step of the release process is being often overlooked, which makes the next release start by merging any changes made in the release branch back to master.
To make this easier and less likely to happen we can just create a PR to merge from release-candidate or release back to master automatically.

How

We run a workflow to build the docker container when a tag vX.X.X or vX.X.X-rc.X is pushed, we can add a step in this workflow to create a PR merging the release (in case of vX.X.X) or release-candidate (in case of vX.X.X-rc.X) to master.

This can be achieved by using the github cli available, the command gh pr create (docs) can easily create the PR, assign the user that signed the tag, add it to the "Hathor Network" project and add a title and body that makes sense for the PR.

[tuliomir]

Another good workflow candidate is the apidocs-upload.yml, that also interacts with version labels.

[pedroferreira1]

I like the proposal and it's really important for us right now, given the previous mistakes we've made. I like the approach of creating this automatic PR and adding to our projects.