feat(experimental-ec2-pattern): Add `buildIdentifier` prop

What does this change?

A requirement of using GuEc2AppExperimental is the filename of the application artifact should include the build identifier. Adding a required buildIdentifier prop to GuEc2AppExperimental uses the type-system to enforce the requirement.

This change also adds a gu:build-identifier tag to the launch template, meaning launched instances receive this tag, improving observability. Furthermore, if instance logs are shipped with devx-logs then this tag becomes a marker on the log lines in Central ELK.

How to test

See updated snapshot.

How can we measure success?

Improved observability.

Have we considered potential risks?

N/A.

Checklist

[ ] I have listed any breaking changes, along with a migration path [^1]
[x] I have updated the documentation as required for the described changes [^2]

[^1]: Consider whether this is something that will mean changes to projects that have already been migrated, or to the CDK CLI tool. If changes are required, consider adding a checklist here and/or linking to related PRs. [^2]: If you are adding a new construct or pattern, has new documentation been added? If you are amending defaults or changing behaviour, are the existing docs still valid?

guardian / cdk