feat: shellcheck Docker scripts, fix warnings

* Warnings were:
In Docker/start_server.sh line 4:
declare -r application_configs="$(ls -d /etc/config/* 2>/dev/null | paste -sd ',' -)"
           ^-----------------^ SC2155 (warning): Declare and assign separately to avoid masking return values.
                                  ^-----------------------------^ SC2012 (info): Use find instead of ls to better handle non-alphanumeric filenames.

docker/start_server.sh

@@ -1,7 +1,8 @@
 #!/bin/bash
 set -euo pipefail
 
-declare -r application_configs="$(ls -d /etc/config/* 2>/dev/null | paste -sd ',' -)"
+application_configs="$(find /tmp/config -mindepth 1 -maxdepth 1 2>/dev/null | paste -sd ',' -)"
+declare -r application_configs
 
 "java" \
   "-Djava.security.egd=file:/dev/urandom" \

scripts/lint.sh

@@ -9,7 +9,7 @@ function go_to_project_root_directory() {
 }
 
 function lint_scripts() {
-    shellcheck scripts/*.sh
+    shellcheck -- */*.sh
 }
 
 function lint_jvm_language_code() {