[sdk] Support artifact custom types in V2 compatible mode

[zijianjoy]

Reference: #5668
Blocks: #3970

In KFP v1, we log output artifact types to MLMD as annotated in DSL. KFP UI can use it to visualize HTML, Markdown, etc as planned in #3970. However, in KFP v2 compatible mode, such artifact type is system.Artifact. We are not able to retrieve type name from component definition in UI.

In order to support visualization compatibility in V2 compatible mode, we need to support custom artifact types from SDK. Once UI can retrieve artifact type from MLMD, we can visualize HTML/Markdown according to the artifact type.

cc @Bobgy @Ark-kun

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[Bobgy]

Thank you @zijianjoy! for starting the issue

slightly adjusting some wordings

[Bobgy]

Several options for open discussion:

• Add new system artifact types for HTML, Markdown, etc in https://github.com/kubeflow/pipelines/blob/master/sdk/python/kfp/dsl/io_types.py.
• Use duck typing to determine type, e.g. if metadata.type == 'HTML', we treat it as HTML artifact.

[Ark-kun]

Use duck typing to determine type, e.g. if metadata.type == 'HTML', we treat it as HTML artifact.

Perhaps we can start with this.

We'll need the ability to preserve the original types names for all custom artifact types, so adding system types might not be feasible or scalable.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[zijianjoy]

We have determined to use HTML and Markdown types.