Automatically add docker containers

**Is your feature request related to a problem? Please describe.**
Adding a new docker container manually to peekaping when deploying is tedious and prone to being forgotten.

**Describe the solution you'd like**
A method of automatically adding a docker container to peekaping would be amazing. This would allow the monitor to be created if the appropriate tags are added like https://github.com/BigBoot/AutoKuma does with UptimeKuma. In the case of AutoKuma this is a bit of a workaround and is prone to issues.

**Describe alternatives you've considered**
Adding a docker host could just add all containers as monitors but this would possibly lead to unwanted monitors. Also adding the containers as docker monitors just monitors whether the container is running, using labels as AutoKuma does would allow the specfic endpoint to be monitored as required.

Look for existing Docker integration code, likely in a directory like `internal/docker` or `pkg/docker`. Understand how monitors are currently created and stored. The feature requires parsing Docker container labels and automatically creating corresponding monitor configurations. Check for any existing tests related to Docker to understand the codebase's patterns.

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