Add arm32 (armv7) support

[e-dong]

Please consider adding arm32/v7 tags to the official docker image on the hub:
https://hub.docker.com/r/jgraph/drawio

Level of effort seems minimal fortunately from my testing.

Current Workaround

Run the following on an armv7 system:

1. Update the base image with a arm32/v7 tag
   E.g.

   adoptopenjdk/openjdk11:jdk-11.0.16.1_1-slim
   

2. Build a new image

   docker build -t drawio:arm32-local ./main
   

3. Create a running container

   docker run -it --rm --name="draw" -p 8080:8080 -p 8443:8443 drawio:arm32-local