Override healthcheck for graphql

[mlutfy]

Implements the solution proposed by @ben-ba to fix #367: failing graphql-server healthcheck

Disclaimer: I'm not an expert on this topic. I was trying BBB for the first time, and noticed this issue.

Before: the container shows unhealthy:

$ docker ps                                                                                                                                                                                                                                                   
CONTAINER ID   IMAGE                                                    COMMAND                  CREATED          STATUS                      PORTS  NAMES
[...]
d0d07eea3024   alangecker/bbb-docker-graphql-server:v3.0.19             "/entrypoint.sh /app…"   17 minutes ago   Up 17 minutes (unhealthy)       bbb-docker-bbb-graphql-server-1         

After: shows healthy:

$ docker ps
CONTAINER ID   IMAGE                                                    COMMAND                  CREATED          STATUS                   PORTS   NAMES
[...]
9e301b6e8f43   alangecker/bbb-docker-graphql-server:v3.0.19             "/entrypoint.sh /app…"   2 minutes ago    Up 2 minutes (healthy)    graphql-server-1