[openapi] Add search fields to all list endpoints

[dhirajsb]

Is your feature request related to a problem? Please describe.
Add search fields to leverage filter_query field in mlmd to allow REST API users to search by most important fields in the element types of each list endpoint.

Describe the solution you'd like
Add most important fields as search parameters, e.g. for Artifacts support searching by name, url, custom_properties etc. The implementation can restrict itself to a single comparison operator ILIKE for simplicity, since it's most commonly used.

Describe alternatives you've considered
None

Additional context
Model Registry users may have a very large number of Models, Version, etc. which they need to be able to search and list efficiently.

[dhirajsb]

@tarilabs @Al-Pragliola @isinyaaa wdyt?