Linux CI builds using WoodpeckerCI

[JulianGro]

I thought I should document somewhere, what issues I am waiting on getting fixed before I start working on automated Linux builds on WoodpeckerCI again.

• Extremely common WoodpeckerCI server crash: "Unknown error occurred" if pipeline step has no output woodpecker-ci/woodpecker#986
• WoodpeckerCI doesn't build multiple platforms simultaneously (rather it waits for one to finish before the other starts): Use multiple agents if matrix platform is used woodpecker-ci/woodpecker#1059
• WoodpeckerCI waits for jobs to finish indefinitely that have already failed: Failed pipeline keeps being shown as running woodpecker-ci/woodpecker#1061
• A feature we require isn't available in any stable versions yet (should be included in version 1.0 once that comes out): Add agent tagging / filtering for pipelines  woodpecker-ci/woodpecker#902