Fixes fluentd/fluent-bit image build CI workflows

[joshuabaird]

What this PR does / why we need it:

#1246 implemented changes that allow us to release "patch" releases of our fluent-bit and fluentd images, but it had a few bugs which are addressed in this PR.

Primarily, the logic that promotes and copies images to Dockerhub was broken for various reasons. This PR centralizes the management of patch tags (eg, 3.1.0-0) and removes some unnecessary checks/complexity. This ensures that there is consistent versioning across all tags/patch releases.

[joshuabaird]

Instead of "determining" the tabs in each "metadata" step -- we just do it once at the top of the workflow and then reference the outputs (tags) in other steps. This ensures that the tags are propagated correctly when copying the images from GHCR to Dockerhub.

[joshuabaird]

As implemented, this check doesn't really provide any value because it's just checking to see if latest exists, and not that the tag that needs to be copied actually exists. I decided to remove it entirely, since the next step which actually tries to copy the image will fail if the image does not exist.

[benjaminhuo]

@joshuabaird Great! Thanks!

[benjaminhuo]

Ops, looks like there're some issues https://github.com/fluent/fluent-operator/actions/runs/10086655163
@joshuabaird

[joshuabaird]

Hmm. I'll take a look this morning.