Fix annotations and label processing

[ptitzler]

Fixes various issues related to kubernetes pod label and annotations processing.

What changes were proposed in this pull request?

• Treat empty label values and empty annotations values as valid input
• Added missing annotations tests
• Updated existing labels tests

How was this pull request tested?

• Updated server tests
• Reviewed the output of kubectl describe pod ... to confirm that labels (prefix.org/lk1, prefix.org/lk2, prefix/lk3) and annotations (ak1, prefix/ak2, ak3) are set as expected for custom components and generic components

$ kubectl describe pod -n kubeflow-user-example-com lambda-bw9rk-440379885
Name:             lambda-bw9rk-440379885
Namespace:        kubeflow-user-example-com
Priority:         0
Service Account:  default-editor
Node:             cloning1.fyre.ibm.com/9.30.189.14
Start Time:       Tue, 04 Oct 2022 09:36:06 -0700
Labels:           pipeline/runid=b97f3544-2b1a-460e-bd3c-b9a26f2b1538
                  pipelines.kubeflow.org/cache_enabled=true
                  pipelines.kubeflow.org/cache_id=
                  pipelines.kubeflow.org/enable_caching=true
                  pipelines.kubeflow.org/kfp_sdk_version=1.8.13
                  pipelines.kubeflow.org/metadata_context_id=8
                  pipelines.kubeflow.org/metadata_execution_id=14
                  pipelines.kubeflow.org/metadata_written=true
                  pipelines.kubeflow.org/pipeline-sdk-type=kfp
                  prefix.org/lk1=1
                  prefix.org/lk2=
                  prefix/lk3=lv3-is-the-value
                  workflows.argoproj.io/completed=true
                  workflows.argoproj.io/workflow=lambda-bw9rk
Annotations:      ak1: 
                  ak3: av3
                  pipelines.kubeflow.org/arguments.parameters: {"URL": "https://www.google.com"}
                  pipelines.kubeflow.org/component_ref: {"digest": "8e4384f422a088e4814024df7955e952c1488bd091fa0d4873d5f611d741ceb4"}
                  pipelines.kubeflow.org/component_spec:
                    {"description": "Downloads a file from a public HTTP/S URL using a GET request.", "implementation": {"container": {"command": ["python3", ...
                  pipelines.kubeflow.org/execution_cache_key: 0001ef28c66b445b3629d5df1db2ca146a0287fc0c90b92880ca26ef4fdf79cc
                  pipelines.kubeflow.org/metadata_input_artifact_ids: []
                  pipelines.kubeflow.org/metadata_output_artifact_ids:
                    [{"id": 22, "name": "downloaded-file", "uri": "minio:///artifacts/lambda-bw9rk/2022/10/04/lambda-bw9rk-440379885/download-file-downloaded-...
                  pipelines.kubeflow.org/task_display_name: Download File
                  prefix/ak2: 0
                  sidecar.istio.io/inject: false

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[elyra-bot]

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[kiersten-stokes]

LGTM! All validation scenarios working as expected, as are empty labels and annotations