Enable MySQL slow query log for performance diagnostics

Add slow_query_log=ON, long_query_time=2, log_queries_not_using_indexes=ON
to capture queries exceeding 2 seconds or performing full table scans.

Closes #76

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: szachovy

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Dependabot updates for `github-actions` and `terraform` ecosystems. (#29)
 * CI workflow to build and push service images to GitHub Container Registry on master merge. (#97)
 * Pull-first with local build fallback for container images during deployment. (#97)
+* MySQL slow query log for queries exceeding 2 seconds or not using indexes. (#76)
 
 ### Changed
 

services/mysql-server/mysql_config.cnf.tpl

@@ -14,3 +14,7 @@ ssl-key = "/etc/mysql/ssl/mysql_server_key.pem"
 require_secure_transport = "ON"
 max_connections = "50"
 max_connect_errors = "50"
+slow_query_log = "ON"
+long_query_time = "2"
+log_queries_not_using_indexes = "ON"
+slow_query_log_file = "/var/log/mysql/slow-queries.log"