Add time and severity to log messages in entrypoint

[webdevred]

This adds a log function which prints a timestamp
that is formatted the same way as the log output
from Fuseki.

I replaced all relevant uses of echo with my new function.

[webdevred]

I am happy to receive any feedback.
Would it make sense to put the log function in a separate file, source it in docker-entrypoint.sh and use it in load.sh as well?
I would actually prefer a format like "2024-11-27 13:31:38" more than "13:31:38" but I am currently not sure how we could change the logging format for the Fuseki server. I think having a universal logging format for messages in the container log would be a nice improvement for when analyzing the logs.
Thanks in advance for your time!

[webdevred]

I took some pictures =)