fix(bff): correctly forward errors from MR API on Get operations

[ederign]

Description

HTTP Get operations from BFF were not forwarding errors correctly.

In this PR:

• clients/ui/bff/internal/integrations/http.go: generated proper error object when there is an error with get operation
• clients/ui/bff/internal/integrations/http_test.go: test coverage for http.go

How Has This Been Tested?

1-) Run model registry with docker compose -f docker-compose.yaml up
2-) Run BFF with make run MOCK_K8S_CLIENT=true MOCK_MR_CLIENT=false
3-) After this PR, we should:

curl -i -H "kubeflow-userid: [email protected]" "localhost:4000/api/v1/model_registry/model-registry-bella/registered_models?namespace=bella-namespace"

HTTP/1.1 200 OK
Content-Type: application/json
Date: Wed, 26 Feb 2025 22:20:18 GMT
Transfer-Encoding: chunked 

If we manually stop mlmd-server from Model Registry (forcing them return a error):

HTTP/1.1 500 Internal Server Error
Content-Type: application/json
Date: Wed, 26 Feb 2025 22:20:59 GMT
Content-Length: 119

{
	"error": {
		"code": "500",
		"message": "the server encountered a problem and could not process your request"
	}
}

I've also done a small sanity check on the UI

Merge criteria:

• All the commits have been signed-off (To pass the DCO check)

• The commits have meaningful messages; the author will squash them after approval or in case of manual merges will ask to merge with squash.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work.
• Code changes follow the kubeflow contribution guidelines.

[google-oss-prow]

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[ederign]

@alexcreasy this will be a quick review in a area of your knowledge.

@christianvogt as you reproduced this, if you also want to look at it!

[adysenrothman]

Tested this locally on my end and everything looks great. Good catch on the gap between MR server failure and BFF resp. /lgtm