Adds remaining endpoints for UI PoC

[alexcreasy]

Description

• Improves API test accuracy and simplicity - tests now go through the full router handler to validate the URL etc.
• Adds many more endpoints, including all required for first UI PoC -- see the updated README for details including example curls for testing
• All Endpoints work in mock mode
• All Endpoints aside from PATCH endpoints work in live cluster

How Has This Been Tested?

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.

If you have UI changes

• The developer has added tests or explained why testing cannot be added.
• Included any necessary screenshots or gifs if it was a UI change.
• Verify that UI/UX changes conform the UX guidelines for Kubeflow.

[alexcreasy]

/hold

[alexcreasy]

/unhold

[Griffin-Sullivan]

Not a super comprehensive review, but I did test the mocks are working and changes look fine to me. Lots of test improvements so I'm not to worried about this one since we will be heavily testing things manually as we develop the UI.

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ederign, Griffin-Sullivan

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• clients/ui/OWNERS [ederign]

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[ederign]

/lgtm