fix: Allow running with environment variables only

The application would previously error out if the config file was not found, even when environment variables were provided. This was because the Dockerfile specified a default config file path, which made the application believe a config file was explicitly required.

This change modifies the config loading logic to only error out if a config file is explicitly specified but not found, and removes the default config file path from the Dockerfile.

Author: google-labs-jules[bot]

Dockerfile

@@ -21,7 +21,6 @@ ENV GITHUB_SERVER=""
 ENV GITLAB_SERVER=""
 ENV LOCAL_GIT_PATH=/var/lib/gobookmarks/localgit
 ENV GOBM_ENV_FILE=/etc/gobookmarks/gobookmarks.env
-ENV GOBM_CONFIG_FILE=/etc/gobookmarks/config.json
 EXPOSE 8080
 EXPOSE 8443
 COPY gobookmarks /bin/gobookmarks