fix: Reduce MySQL binlog expiry from 30 days to 3

MySQL 8 defaults to a binlog expiry period of 2592000 seconds
(30 days), which for Tutor/Open edX purposes can be considered
excessive.

On the one hand, it is unlikely that a MySQL server configured for
Tutor uses MySQL replication at all (considering that up until Tutor
15 and MySQL 5.7, the binlog was disabled by default, rendering
replication impossible). Even if it does, a replica lagging more than
two days behind the primary server would be unacceptable.

Likewise, it is unlikely that an Open edX database is backed up less
than once a day, thus is is unlikely that Open edX admins would
benefit from the ability to do point-in-time restore over a 30-day
period.

On the other hand, having a 30-day binlog expiry period can
considerably increase the storage space requirements for the MySQL
container, particularly on busy Open edX platforms. When left
unchecked, this can even cause the MySQL container to run into "No
space left on device" situations, disabling the MySQL database
altogether. Thus, the MySQL default settings are likely to be a net
disadvantage for Open edX admins.

Finally, all of the above considerations apply only if the Open edX
administrator has chosen to run their own MySQL and not opted for a
DBaaS solution like AWS RDS.

Thus, it should be acceptable to run with a reduced binlog expiry
period of 3 days (rather than 30) by default.

Therefore, inject the --binlog-expire-logs-seconds=259200 argument
into the Tutor-generated command to start mysqld.

Reference:
https://dev.mysql.com/doc/refman/8.0/en/replication-options-binary-log.html#sysvar_binlog_expire_logs_seconds

changelog.d/20231023_155558_fghaas_binlog_expiry.md

@@ -0,0 +1 @@
+[Improvement] When configured with `RUN_MYSQL: true`, run `mysqld` with binlog expiry set to 3 days (rather than the default of 30).

tutor/templates/k8s/deployments.yml

@@ -392,7 +392,11 @@ spec:
       containers:
         - name: mysql
           image: {{ DOCKER_IMAGE_MYSQL }}
-          args: ["mysqld", "--character-set-server=utf8mb3", "--collation-server=utf8mb3_general_ci"]
+          args:
+            - "mysqld"
+            - "--character-set-server=utf8mb3"
+            - "--collation-server=utf8mb3_general_ci"
+            - "--binlog-expire-logs-seconds=259200"
           env:
             - name: MYSQL_ROOT_PASSWORD
               value: "{{ MYSQL_ROOT_PASSWORD }}"

tutor/templates/local/docker-compose.yml

@@ -40,7 +40,11 @@ services:
   {% if RUN_MYSQL -%}
   mysql:
     image: {{ DOCKER_IMAGE_MYSQL }}
-    command: mysqld --character-set-server=utf8mb3 --collation-server=utf8mb3_general_ci
+    command: >
+      mysqld
+      --character-set-server=utf8mb3
+      --collation-server=utf8mb3_general_ci
+      --binlog-expire-logs-seconds=259200
     restart: unless-stopped
     user: "999:999"
     volumes: