Add pnpm command to update snapshot

[aurelius0523]

Overview

Add a new pnpm test:template:updateSnapshot script

What it does

It leverages existing update-template.sh and adds a -u option to update snapshot. It will update existing snapshots when running tests in tmp-${template} dir and copy the snapshots to skuba/template dir

Why

To make it easier to avoid #1646 because I missed it in #1644

Further thoughts

I initially thought to make pnpm test:template --updateSnapshot by default but I am unsure of the existing approach. Assuming that snapshots in template are meant as safeguard for template user and not skuba developers, it might be easier to just have a husky pre-commit hook to --updateSnapshot by default when modifying templates.

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Latest commit: b5e98ef

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[AaronMoat]

I think I was silly and force merged when I shouldn't have. I think I thought they were failing from the fork, but looking at the build again it seems fairly obvious why it failed.

But: For development this is FANTASTIC, thank you!

I believe the snapshots for the CDK template are actually intended for the developer (as well); if a developer takes the template, makes changes, and so on - it's nice to get a diff in the tests / PR for what infrastructure is changing. There are of course other ways we could do this (e.g. staging a changeset)