Add pkg.dev to automagic config file population

[jonjohnsonjr]

Description

Kaniko currently does config file setup for GCR such that pushing to GCR
automagically works. This change does the same for pkg.dev:
https://cloud.google.com/artifact-registry

This also tightens up the hostname check to ensure we don't send
credentials to a registry that happens to contain "gcr.io".

This uses the --registries flag from docker-credential-gcr to configure only the registry we actually care about, instead of just blindly calling docker-credential-gcr configure-docker, which configures every domain. An alternative approach to this PR would be to add pkg.dev domains to the list of domains that docker-credential-gcr configure-docker configures by default (see GoogleCloudPlatform/docker-credential-gcr#68), but that has the unfortunate side effect of making docker build really slow (it fetches credentials for every configured registry), which we want to avoid.

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Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.