feat: support LOG_CONFIG environment variable

This variable allows users to override the logging.conf used
for Python logging configuration. By default, this is set
to logging.conf, which is a production config. LOG_CONFIG
is treated relative to [options] aurwebdir.

This patch allows us to specify the logging config as opposed
to copying over logging.conf in our test docker and gitlab
test scripts, as well as ease-of-testing as a developer.

Signed-off-by: Kevin Morris <kevr@0cost.org>

docker/sharness-entrypoint.sh

@@ -1,6 +1,4 @@
 #!/bin/bash
 set -eou pipefail
 
-cp -vf logging.prod.conf logging.conf
-
 exec "$@"

docker/test-mysql-entrypoint.sh

@@ -1,9 +1,6 @@
 #!/bin/bash
 set -eou pipefail
 
-# Set test logging.
-cp -vf "logging.test.conf" "logging.conf"
-
 # We use the root user for testing in Docker.
 # The test user must be able to create databases and drop them.
 aurweb-config set database user 'root'