calibre: make entrypoint more generic

[stavros-k]

I'm not sure why it was /storage/elfstorage but volume was /media.
Let me know if you want to switch that back or update the volume.

Added a check that if a metadata.db is missing (eg if you mount a bind volume on top of the already created directory in the dockerfile)
Added variables for port and trusted IPs.

[stavros-k]

With this as an entrypoint, I got it to work fine.

if [ ! -f /books/metadata.db ]; then
  echo 'Creating an empty calibre metadata database at [/books/metadata.db]'
  touch /books/metadata.db
fi

/usr/bin/calibre-server \
  --port=8085 \
  --enable-local-write \
  --disable-use-bonjour \
  --trusted-ips=192.168.0.0/16,172.16.0.0/12,10.0.0.0/8 \
  /books

I do see this

No write access to /home/elfie/.config/calibre using a temporary dir instead

But does not seem to affect usage.

If I set HOME=/tmp/home, the error goes away, but I don't see anything that needs to be persisted anyway.
I'm not sure if home is used for something else in the image and I don't want to "mess it up"

[github-actions]

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