Simplify kepler image

[dommyrock]

Simplify kepler image

Simplified kepler dockerfile and updated DOCS to use docker exec instead of creating new container and than running commands in it with docker run.

I ran some tests using these podman commands to make sure importing was still working the same way as before.

podman exec -it kepler kepler import_nist 2025 -d /data

for year in $(seq 2002 2025); do
  podman exec -it  kepler kepler import_nist $year -d /data
done

REFS

• https://docs.docker.com/reference/cli/docker/container/run/
• https://docs.docker.com/reference/cli/docker/container/exec/

I have

• run cargo fmt;
• run cargo clippy;
• run cargo testand all tests pass;
• linked to the originating issue (if applicable).

[dommyrock]

Cc @davidristov just want to make sure you're ok with these changes before merging ?