Update metrics schema

### Is your feature request related to a problem? Please describe.

Having a catalog name and table identifier(namespace.table) would benefit the metrics query so that no join is needed in most use cases. It could be especially useful when metrics and Polaris entity are in different data sources or even different type of databases, like Prometheus vs Postgres.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by locating the metrics schema and query implementation, then review how Polaris entities are joined to metrics across data sources. Determine where catalog name and namespace.table should be represented and define the expected query behavior; done means the schema supports those identifiers without requiring the usual join.

Written by the indexing model from the issue text.