chore: remove unused code with MetricBase

[silenceqi]

What does this PR do

This pull request includes significant changes to the insight module, primarily focusing on the removal of the MetricBase type and associated API endpoints. The changes also involve cleaning up imports and schema registrations related to the removed type.

Removal of MetricBase type and associated API endpoints:

• model/insight/metric_data.go: Removed the MetricBase type definition and its associated fields.
• plugin/api/insight/api.go: Removed API endpoints for creating, updating, and deleting metrics.
• plugin/api/insight/metric.go: Deleted the entire file, which contained the implementation of the metric-related API endpoints.

Cleanup of imports and schema registrations:

• main.go: Removed the schema registration for MetricBase.
• model/insight/metric_data.go: Removed the import of orm since it is no longer needed.
• plugin/api/platform/domain.go: Removed imports and collection metadata related to MetricBase. [1] [2]

Rationale for this change

Standards checklist

• The PR title is descriptive
• The commit messages are semantic
• Necessary tests are added
• Updated the release notes
• Necessary documents have been added if this is a new feature
• Performance tests checked, no obvious performance degradation