Add support of bazel tags to rules_gitops

Description

Add ability to use bazel tags on k8s_deploy targets so can use bazel tag filters on these targets to include or exclude from building.

Motivation and Context

This enables including or excluding k8s_deploy targets based on build tag filters as well as other common tag based bazel operations like bazel query.

In particular, containers can be expensive to build. I can tag my container_images and then use build tag filters to ignore building those, but if they are used in a k8s_deploy, they cannot be excluded through a tag filter.

How Has This Been Tested?

I've tested this in my own project via

using a tag filter (e.g. --build_tag_filter=-excluded)
making sure if the container was built, it would fail (e.g. bad code)
having the "excluded" tag on both the container_image and k8s_deploy target

Also, I added usage of tags to the helloworld example for basic smoke test of functionality

Without this change, it would fail building (bazel build --build_tag_filter=-excluded //...), while with this change, it would pass with the same command.

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[x] I have signed the Adobe Open Source CLA.
[ ] My code follows the code style of this project.
[x] My change requires a change to the documentation.
[x] I have updated the documentation accordingly.
[x] I have read the CONTRIBUTING document.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.

adobe / rules_gitops