fix: patch requests to artifact endpoint make mr panic

[Al-Pragliola]

Description

Trying to do a PATCH request to v1alpha3/artifacts/{artifactId} made mr panic:

http: panic serving 0.0.0.0:8080: runtime error: invalid memory address or nil pointer dereference
goroutine 25997 [running]:
net/http.(*conn).serve.func1()
	/usr/lib/golang/src/net/http/server.go:1873 +0xb9
panic({0xb13ba0?, 0x13a8810?})
	/usr/lib/golang/src/runtime/panic.go:920 +0x270
github.com/kubeflow/model-registry/internal/server/openapi.(*ModelRegistryServiceAPIService).UpdateArtifact(0xc0003c7c20, {0xb351a0?, 0xc000042190?}, {0xc00029e0ad, 0x1}, {0x0, 0x0})
	/workspace/internal/server/openapi/api_model_registry_service_service.go:496 +0x12f
github.com/kubeflow/model-registry/internal/server/openapi.(*ModelRegistryServiceAPIController).UpdateArtifact(0xc000013c98, {0x7fb4fa6124b8, 0xc0001665c0}, 0xc0001d8e00)
	/workspace/internal/server/openapi/api_model_registry_service.go:902 +0x1cd
net/http.HandlerFunc.ServeHTTP(0xb0e3c0?, {0x7fb4fa6124b8?, 0xc0001665c0?}, 0xc00029e086?)
	/usr/lib/golang/src/net/http/server.go:2141 +0x29
github.com/go-chi/chi/v5.(*Mux).routeHTTP(0xc0003b8de0, {0x7fb4fa6124b8, 0xc0001665c0}, 0xc0001d8e00)
	/cachi2/output/deps/gomod/pkg/mod/github.com/go-chi/chi/[email protected]/mux.go:459 +0x2b4
net/http.HandlerFunc.ServeHTTP(0xc0000cc960?, {0x7fb4fa6124b8?, 0xc0001665c0?}, 0xc0001d8e00?)
	/usr/lib/golang/src/net/http/server.go:2141 +0x29
github.com/go-chi/cors.(*Cors).Handler-fm.(*Cors).Handler.func1({0x7fb4fa6124b8, 0xc0001665c0}, 0xc0001d8e00)
	/cachi2/output/deps/gomod/pkg/mod/github.com/go-chi/[email protected]/cors.go:228 +0x17e
net/http.HandlerFunc.ServeHTTP(0xc0001d8d00?, {0x7fb4fa6124b8?, 0xc0001665c0?}, 0x30?)
	/usr/lib/golang/src/net/http/server.go:2141 +0x29
github.com/go-chi/chi/v5/middleware.init.0.RequestLogger.func1.1({0xd08058, 0xc00019a540}, 0xc0001d8d00)
	/cachi2/output/deps/gomod/pkg/mod/github.com/go-chi/chi/[email protected]/middleware/logger.go:55 +0x16d
net/http.HandlerFunc.ServeHTTP(0xd09790?, {0xd08058?, 0xc00019a540?}, 0x13a92c0?)
	/usr/lib/golang/src/net/http/server.go:2141 +0x29
github.com/go-chi/chi/v5.(*Mux).ServeHTTP(0xc0003b8de0, {0xd08058, 0xc00019a540}, 0xc0001d8c00)
	/cachi2/output/deps/gomod/pkg/mod/github.com/go-chi/chi/[email protected]/mux.go:90 +0x330
net/http.serverHandler.ServeHTTP({0xd05f10?}, {0xd08058?, 0xc00019a540?}, 0x6?)
	/usr/lib/golang/src/net/http/server.go:2943 +0x8e
net/http.(*conn).serve(0xc0001b7560, {0xd09758, 0xc0003d62d0})
	/usr/lib/golang/src/net/http/server.go:2014 +0x5f4
created by net/http.(*Server).Serve in goroutine 1
	/usr/lib/golang/src/net/http/server.go:3091 +0x5cb 

How Has This Been Tested?

curl -k -X 'POST' 'http://localhost:8080/api/model_registry/v1alpha3/artifacts' -d '{"description": "test","artifactType": "model-artifact"

curl -k -X 'PATCH' 'http://localhost:8080/api/model_registry/v1alpha3/artifacts/1' -d '{"description": "test-two","artifactType": "model-artifact"}'

plus

python client e2e tests

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.

[tarilabs]

thank you so much for the PR @Al-Pragliola but also especially for adding a py non-regression test!!

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tarilabs

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