Add support for Google Artifact Registry (GAR) (#692)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following PR:
* Deprecates the existing OCI reference parser
* Deprecates the existing OCI way of authenticating and accessing the
image manifest
* Replaces the above by leveraging go-containerregistry
* Introduces support for Google Artifact Registry
* Enables us to easily add support for other OCI-compliant registries in
the future
* Introduces better error handling
* Introduces custom context timeouts for validation 

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] 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)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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-->
Related to #427

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

go.mod

@@ -6,10 +6,11 @@ require (
 	github.com/caarlos0/env/v11 v11.3.1
 	github.com/coreos/go-oidc/v3 v3.16.0
 	github.com/danielgtaylor/huma/v2 v2.34.1
-	github.com/distribution/reference v0.6.0
 	github.com/golang-jwt/jwt/v5 v5.3.0
+	github.com/google/go-containerregistry v0.20.6
 	github.com/jackc/pgx/v5 v5.7.6
 	github.com/prometheus/client_golang v1.23.2
+	github.com/rs/cors v1.11.1
 	github.com/santhosh-tekuri/jsonschema/v5 v5.3.1
 	github.com/stretchr/testify v1.11.1
 	go.opentelemetry.io/contrib/instrumentation/runtime v0.63.0
@@ -25,7 +26,11 @@ require (
 require (
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/containerd/stargz-snapshotter/estargz v0.16.3 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/docker/cli v28.2.2+incompatible // indirect
+	github.com/docker/distribution v2.8.3+incompatible // indirect
+	github.com/docker/docker-credential-helpers v0.9.3 // indirect
 	github.com/go-jose/go-jose/v4 v4.1.3 // indirect
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
@@ -34,14 +39,19 @@ require (
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/klauspost/compress v1.18.0 // indirect
+	github.com/mitchellh/go-homedir v1.1.0 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
+	github.com/opencontainers/image-spec v1.1.1 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/client_model v0.6.2 // indirect
 	github.com/prometheus/common v0.66.1 // indirect
 	github.com/prometheus/otlptranslator v0.0.2 // indirect
 	github.com/prometheus/procfs v0.17.0 // indirect
-	github.com/rs/cors v1.11.1 // indirect
+	github.com/sirupsen/logrus v1.9.3 // indirect
+	github.com/vbatts/tar-split v0.12.1 // indirect
 	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
 	go.opentelemetry.io/otel/trace v1.38.0 // indirect
 	go.yaml.in/yaml/v2 v2.4.2 // indirect