optimize ci build: use own dockerfile for dependencies + cache for builds (#164)

Reviewed-on: Ruderverein-Donau-Linz/rowt#164

Dockerfile

@@ -0,0 +1,26 @@
+# This dockerfile is used as basis for the CI jobs.
+# Process to renew it:
+# 0. Login to gitea docker registry: `docker login git.hofer.link`
+# 1. Build the image `docker build .`
+# 2. Tag the image: `docker tag <id> git.hofer.link/ruderverein-donau-linz/rowing-ci:<date>`
+# 3. Push the image: `docker push git.hofer.link/ruderverein-donau-linz/rowing-ci:<date>`
+
+
+FROM rust:1.75.0
+
+RUN apt-get update && apt-get install -y sqlite3
+
+# nodejs
+RUN apt-get install -y curl && \
+    curl -sL https://deb.nodesource.com/setup_21.x | bash - && \
+    apt-get install -y nodejs
+
+# playwright
+RUN npx playwright install --with-deps
+
+# deployment
+RUN rustup target add x86_64-unknown-linux-musl
+RUN apt-get install -y -qq pkg-config sshpass musl musl-tools curl gnupg libssl-dev
+
+# TEMPORARY act workaround (otherwise gitea cache is not working)
+RUN apt-get install -y zstd