server: allow every config value to be specified as a file

By using https://crates.io/crates/figment_file_provider_adapter

Fixes https://github.com/nitnelave/lldap/issues/263

docker-entrypoint.sh

@@ -1,20 +1,6 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-for SECRET in LLDAP_JWT_SECRET LLDAP_LDAP_USER_PASS LLDAP_SMTP_OPTIONS__PASSWORD; do
-    FILE_VAR="${SECRET}_FILE"
-    SECRET_FILE="${!FILE_VAR:-}"
-    if [[ -n "$SECRET_FILE" ]]; then
-        if [[ -f "$SECRET_FILE" ]]; then
-            declare "$SECRET=$(cat $SECRET_FILE)"
-            export "$SECRET"
-            echo "[entrypoint] Set $SECRET from $SECRET_FILE"
-        else
-            echo "[entrypoint] Could not read contents of $SECRET_FILE (specified in $FILE_VAR)" >&2
-        fi
-    fi
-done
-
 CONFIG_FILE=/data/lldap_config.toml
 
 if [[ ( ! -w "/data" ) ]] || [[ ( ! -d "/data" ) ]]; then