Add: docker & gh-actions to dependabot

[GoliathLabs]

Hi, I've added the docker and the gh-actions ecosystem to the dependabot.yml so we get notified if any updated image tags or actions are available. As you're already using this for the go ecosystem, this would be a nice addition I think

[ldez]

Hello,

It's not against you but I boycott dependabot on my projects, this issue must be fixed https://github.com/dependabot/dependabot-core/issues/2804

FYI, currently, the bot is not able to handle the go dependencies of this project