Add endpoint, types and API hooks for MCP server catalog

[ppadti]

Description

This PR aims to add endpoint, types, mocks and api hooks for mcp server catalog.
Need to add unit test for hooks - will be done in follow-up PR.

How Has This Been Tested?

run the application in mock mode and try this curl commands:

List MCP servers

curl -s -H "kubeflow-userid: user@example.com" \ "http://localhost:4000/api/v1/model_catalog/mcp_servers?namespace=kubeflow"

MCP filter options
curl -s -H "kubeflow-userid: user@example.com" \ "http://localhost:4000/api/v1/model_catalog/mcp_servers_filter_options?namespace=kubeflow"

Get a MCP server
curl -s -H "kubeflow-userid: user@example.com" \ "http://localhost:4000/api/v1/model_catalog/mcp_servers/prometheus-mcp?namespace=kubeflow"

MCP server tools
curl -s -H "kubeflow-userid: user@example.com" \ "http://localhost:4000/api/v1/model_catalog/mcp_servers/prometheus-mcp/tools?namespace=kubeflow"

modified source endpoint

curl -s "http://localhost:4000/api/v1/model_catalog/sources?namespace=kubeflow&assetType=models" -H "kubeflow-userid: [user@example.com](mailto:user@example.com)"

curl -s "http://localhost:4000/api/v1/model_catalog/sources?namespace=kubeflow&assetType=mcp_servers" -H "kubeflow-userid: [user@example.com](mailto:user@example.com)"

curl -X GET "http://localhost:4000/api/v1/model_catalog/sources?namespace=kubeflow" \
  -H "kubeflow-userid: user@example.com"

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.
• For first time contributors: Please reach out to the Reviewers to ensure all tests are being run, ensuring the label ok-to-test has been added to the PR.

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.

[google-oss-prow]

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