feat: add dockerfile for debian, alpine

[soulteary]

This project is very useful, but looking through the entire project, no docker image was found.

So I added the dockerfile and update build script.

You can execute the command make release-docker got two docker imgae:

adnanh/webhook        alpine        e9a0f8f7f1e9   10 minutes ago    16MB
adnanh/webhook        latest        72c715fe0d32   10 minutes ago   111MB

Before the PR accept, if anyone wants to experience docker image, you can temporarily use my docker image instead

docker run --rm -it soulteary/webhook:alpine 
# or
docker run --rm -it soulteary/webhook

[soulteary]

Hi, I saw this pull request awaiting a long time, and it seems approved by @AliBK585A a week ago, but the page notice: "First-time contributors need a maintainer to approve running workflows."

Anyone can give a hand? thanks

@adnanh @AliBK585A sorry for disturbing :D