Replace deprecated JDBC driver

[nya-elimu]

We see this in the PROD environment:

jetty[1119]: Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary.

Current version in pom.xml:

  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.28</version>
  </dependency>

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• Relates to @NotNull should also apply to DDL #1702