Add support for Docker default config file

[samj1912]

Fix #871
Fix #872
Fix #606

This PR guts the custom docker image/digest logic and replaces it with GGCR. This allows us to have a robust docker validation logic.

Test

To test this pull request, you can run the following commands:

sources:
  tag:
    kind: dockerimage
    spec:
      image: ghcr.io/updatecli/updatecli
  digest:
    kind: dockerdigest
    spec:
      image: ghcr.io/updatecli/updatecli
      tag: v0.34.0

./dist/updatecli_darwin_arm64/updatecli diff --config config.yaml


+++++++++++
+ PREPARE +
+++++++++++

Loading Pipeline "config.yaml"

SCM repository retrieved: 0


++++++++++++++++++
+ AUTO DISCOVERY +
++++++++++++++++++



++++++++++++
+ PIPELINE +
++++++++++++



###############
# CONFIG.YAML #
###############


SOURCES
=======

digest
------
✔ Docker Image Tag ghcr.io/updatecli/updatecli:v0.34.0 resolved to digest ghcr.io/updatecli/updatecli@sha256:779abc2c7a46c0cc0d568bac6e6d8b81c9b3255bb025a5f421d0911a82e3d4c5

tag
---
Searching for version matching pattern "latest"
✔ Docker Image Tag "v0.34.0" found matching pattern "latest"

=============================

REPORTS:


- CONFIG.YAML:
	Source:
		✔ [digest]  (kind: dockerdigest)
		✔ [tag]  (kind: dockerimage)

Run Summary
===========
Pipeline(s) run:
  * Changed:	0
  * Failed:	0
  * Skipped:	1
  * Succeeded:	0
  * Total:	1

Additional Information

Tradeoff

Potential improvement

[olblak]

Nice work, I didn't realize how far you went. Indeed I need some e2e tests for different registries like ghcr.io dockerhub and quay

[olblak]

I did some initial testing and I didn't find any regression, I need to find some ways to test with other registries than dockerhub or ghcr.io

[olblak]

I confirm that your code fallback to the docker configuration file to retrieve credentials.
I don't have permission to push on your local branch, so I'll probably move forward with your pullrequest and the e2e tests that I have locally

[samj1912]

The only 'regression' might be the registry for how dockerhub is resolved. It will be resolved to index.docker.io

[olblak]

The only 'regression' might be the registry for how dockerhub is resolved. It will be resolved to index.docker.io

Which I don't think is a problem at all. If I recall correctly that URL was needed for the previous code which is now replaced by GGCR

[olblak]

I am renaming the pullrequest to "Add support for Docker default config file" to highlight that this pullrequest is not only a great refactoring by fixing various issues but it's great enhancement that will benefit to autodiscovery feature.

[samj1912]

@olblak fixed the failing registry test and rebased. Should be all good to go now.