Upgrade the app to Java 17

[emmastephenson]

Background

We're currently on Java 11, but Java 17 is the latest LTS version. We should upgrade to 17, especially as this is a prerequisite to adopting Spring 3.0.

Action requested

Upgrade the application to Java 17. Within the application, this should just be a change to our build.gradle, but we'll also need to consider:

• How to upgrade Java versions for local development (intelliJ should at least partially automate this)
• What Azure and Terraform infrastructure needs to be updated, if any

Acceptance Criteria

There shouldn't be breaking changes between Java 11 and Java 17 (one hopes) but we'll need to smoke test the application regardless.

Additional context

See the Java LTS schedule here.

Exciting things about this release

• Text blocks, aka multiline strings, aka triple-quotes!

  String multilineString = "hello \n world";

  now becomes

  String multilineString =
  """ hello
  world
  """;

• less verbose switch statements!
• records, which might enable us to remove some Lombok annotations!
• more helpful NullPointerExceptions! more details about the upgrade features

[emmastephenson]

This will also require us to update the Azure JDK version.

Once this is merged, local development will also need to install the new JDK versions.