RHIDP-9710 Create aggregated metrics API for Scorecard backend plugin

[imykhno]

Hey, I just made a Pull Request!

Improvement aggregation logic after merge the #1984.
In this PR:

• Added another entity to belong to different user as was discussed in RHIDP-9710 Create aggregated metrics API for Scorecard backend plugin #1984 (review)
• Updated aggregations endpoint from /metrics/:metricId/catalog/aggregation to /metrics/:metricId/catalog/aggregations. Ref - RHIDP-9710 Create aggregated metrics API for Scorecard backend plugin #1984 (comment)
• Updated aggregation.md and README.md
• Updated logic for the /metrics endpoint

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or Updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)

[rhdh-gh-app]

Missing Changesets

The following package(s) are changed by this PR but do not have a changeset:

• @red-hat-developer-hub/backstage-plugin-scorecard-backend

See CONTRIBUTING.md for more information about how to add changesets.

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@red-hat-developer-hub/backstage-plugin-scorecard-backend	workspaces/scorecard/plugins/scorecard-backend	none	v2.2.0

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud