Version 0.28.0

[douglas]

What are you trying to accomplish with this PR?

Cut a release that includes:

Important!

• The next release will be 1.0.0, which means that master probably will contain breaking changes.

Enhancements

• Officially support Kubernetes 1.15 (#546)
• Make sure that we only declare a Service of type LoadBalancer as deployed after its IP address is published. #547
• Add more validations to RunnerTask. #554
• Validate secrets with --server-dry-run on supported clusters. #553

Bug Fixes

• Fix a bug in rendering where we failed to add a yaml doc separator (---) to
  an implicit document if there are multiple documents in the file.
  (#551)

Other

• Kubernetes 1.10 is no longer officially supported as of this version (#546)
• We've added a new Krane cli. This code is in alpha. We are providing
  no warranty at this time and reserve the right to make major breaking changes including
  removing it entirely at any time. (#256)
• Deprecate kubernetes-deploy.shopify.io annotations in favour of krane.shopify.io (#539)

How is this accomplished?

Bump version followed by Shipit deploy once this merges

What could go wrong?

Let's do a bit of tophatting before releasing this and make sure everything we want it in the changelog

cc @Shopify/production-excellence