feat(catalog): add sourceLabel filter

[pboyd]

Description

Add sourceLabel query string parameter to the /api/model_catalog/v1alpha1/models endpoint.

How Has This Been Tested?

Local kind cluster and unit tests.

Merge criteria:

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

• The commits have meaningful messages
• Automated tests are provided as part of the PR for major new functionalities; 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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[pboyd]

/retest