Update LocalStack version

[mwarman]

Describe the task

Review the LocalStack image version and update to the latest stable version.

Additional context

n/a

[mwarman]

Updating from version 4.12 to version 2026.03. Note that LocalStack has changed their version naming scheme in 2026.

There are some other changes such as the LOCALSTACK_AUTH_TOKEN always being required, even for the free version of LocalStack.

• Installation Docs
• Auth Token Docs