Add support for Kubernetes stacks

Description of the change

Added support for Kubernetes stacks.
Simplified the stack resource tests for CloudFormation and Pulumi to avoid checking every attribute. That's covered by other tests, and it makes them less clear.
Added data source tests for CloudFormation, Kubernetes and Pulumi and fixed a bug in the CloudFormation settings for the stack data source where it was setting entry_template_name instead of entry_template_file.
Refactored the stack examples to avoid confusion between stacks creating Kubernetes resources vs stacks using the Kubernetes provider.

[ ] Bug fix (non-breaking change that fixes an issue)
[x] New feature (non-breaking change that adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Documentation (non-breaking change that adds documentation)

[x] Lint rules pass locally
[x] The code changed/added as part of this pull request has been covered with tests
[x] All tests related to the changed code pass in development

[x] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
[x] Pull Request is no longer marked as "draft"
[ ] Reviewers have been assigned
[ ] Changes have been reviewed by at least one other engineer
[x] The target branch is future unless the change is going directly into production