Move to use dockerfile for build

Dockerfile

@@ -0,0 +1,5 @@
+FROM git.janishutz.com/registry/latex-build:latest
+
+WORKDIR /root
+
+ENTRYPOINT [ "/root/entrypoint.sh" ]

action.yml

@@ -10,7 +10,7 @@ inputs:
     default: ""
 runs:
   using: docker
-  image: git.janishutz.com/registry/latex-build:latest
+  image: Dockerfile
   args:
     - ${{ inputs.args }}
     - ${{ inputs.extra_system_packages }}