feat: Docker builds

[GoliathLabs]

Description

Adds docker support & proper workflows to automatically build the image.

Motivation and Context

More and more communities are using Docker in their deployments. This makes it possible to package meshviewer as a docker image.

How Has This Been Tested?

In the dev environment over at https://github.com/freifunkMUC/meshviewer

Screenshots/links:

Checklist:

• My code follows the code style of this project. (CI will test it anyway and also needs approval)
• [n/a] My change requires a change to the documentation.
  • [n/a] I have updated the documentation accordingly.

[GoliathLabs]

After #110 has been merged, this can be rebased and merged as well :)

[ronnyhartenstein]

Will this PR ever merged? We'd like to use it for Freifunk Chemnitz and don't want to fork it.
Can we contribute something?
/CC @oliverlorenz

[skorpy2009]

@GoliathLabs can you please update this PR?

[GoliathLabs]

@skorpy2009 done :)

[skorpy2009]

That didn't work out well.

Check failure on line 24 in .github/workflows/build-docker.yml
GitHub Actions / Build Docker image

Invalid workflow file

The workflow is not valid. .github/workflows/build-docker.yml (Line: 24, Col: 14): Unexpected value ''

@GoliathLabs