Add OpenTofu provider OCI artifact integration test

[Copilot]

Description

Adds OpenTofuITCase to demonstrate assembling an OpenTofu provider artifact per the OCI provider mirror spec. The test covers the full assembly flow: a platform-specific manifest pushed to the registry, then referenced in an OCI image index.

New files:

• OpenTofuITCase.java — integration test with shouldAssembleOpenTofuProviderArtifact, following the same pattern as HelmITCase/FluxCDITCase
• terraform-provider-aws_5.0.0_linux_amd64.zip — minimal test fixture simulating a provider binary

Key changes:

• Both the Manifest and the Index use artifactType = "application/vnd.opentofu.provider" so that OpenTofu can recognize them as representing a provider release
• The Config is left as Config.empty() (no media type override)
• Added Index.withArtifactType(String) fluent method to support setting artifact type on an index
• Added unit test IndexTest#shouldAddArtifactType covering the new method

Key flow:

// linux/amd64 manifest with artifactType
Config config = Config.empty();
Layer layer = Layer.fromFile(providerZip).withMediaType("application/zip");
Manifest manifest = Manifest.empty()
        .withArtifactType(ArtifactType.from("application/vnd.opentofu.provider"))
        .withConfig(config)
        .withLayers(List.of(layer));
Manifest pushedManifest = registry.pushManifest(manifestRef, manifest);

// Index referencing the platform manifest, also with artifactType
ManifestDescriptor descriptor = pushedManifest.getDescriptor().withPlatform(Platform.linuxAmd64());
Index index = Index.fromManifests(List.of(descriptor))
        .withArtifactType("application/vnd.opentofu.provider");
Index pushedIndex = registry.pushIndex(indexRef, index);

assertNotNull(pushedIndex.findUnique(Platform.linuxAmd64()));

Testing done

OpenTofuITCase#shouldAssembleOpenTofuProviderArtifact runs against a local Zot registry via Testcontainers, verifying the manifest and index are pushed and the index resolves the linux/amd64 platform entry. IndexTest#shouldAddArtifactType unit-tests the new Index.withArtifactType method.

Submitter checklist

• I have read and understood the CONTRIBUTING guide
• I have run mvn license:update-file-header, mvn spotless:apply, pre-commit run -a, mvn clean install before opening the PR

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[jonesbusy]

@copilot

This part is incorrect The index manifest must have its artifactType property set to application/vnd.opentofu.provider so that OpenTofu can recognize is as a representing a provider release

Please use the artifact type for both Manifest and Index.

Not the config media type (we can leave it empty)

[Copilot]

@copilot

This part is incorrect `The index manifest must have its artifactType property set to application/vnd.opentofu.provider so that OpenTofu can recognize is as a representing a provider rele...

Fixed in 9bf5969. Both Manifest and Index now use artifactType = "application/vnd.opentofu.provider". The config is left as Config.empty() (no media type). I also added Index.withArtifactType(String) to support setting the artifact type on an index and covered it with a unit test in IndexTest.