changing docker file command to entrypoint so we can send arguments

[maayanmord]

When using ENTRYPOINT instead of COMMAND in a Dockerfile, you gain flexibility when running containers with additional parameters:

With COMMAND: You must override the entire command to add flags
With ENTRYPOINT: You can simply append parameters to the base command
This change simplifies how we pass additional flags like --web.listen-address to the sql_exporter.

Before: using COMMAND

docker run \
  -v `pwd`/config.yml:/config/config.yml \
  -e CONFIG=/config/config.yml \
  -d \
  -p 9237:9237 \
  --name sql_exporter \
  ghcr.io/justwatchcom/sql_exporter \
  sql_exporter \
  --web.listen-address :9123

After: using ENTRYPOINT

docker run \
  -v `pwd`/config.yml:/config/config.yml \
  -e CONFIG=/config/config.yml \
  -d \
  -p 9237:9237 \
  --name sql_exporter \
  ghcr.io/justwatchcom/sql_exporter \
  --web.listen-address :9123