Implement limited count for vulnerability severity counts

What does this MR do and why?

• Adds limitedVulnerabilitySeverityCounts field to project, groups and instanceSecurityDashboard GraphQL API.

• We have performance concerns doing full count operation so limiting the counting operation on DB to 1001 records for each severity type. For context see discussion #432715 (comment 1742125731)

• Aim is to use the new GraphQL API on the UI. UI work is tracked in #463387.

Related to #438303

Database

Default dashboard report filter

API	Before (vulnerabilitySeveritiesCount)	After (limitedVulnerabilitySeverityCounts)
Project	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89483	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89485
Group	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89487	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89491
Instance security dashboard	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89468	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89481

Another filter

API	Before (vulnerabilitySeveritiesCount)	After (limitedVulnerabilitySeverityCounts)
Project	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89498	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89500
Group	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89496	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89494
Instance security dashboard	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89502	https://console.postgres.ai/gitlab/gitlab-production-main/sessions/28708/commands/89504

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

vulnerabilitySeveritiesCount	limitedVulnerabilitySeverityCounts

How to set up and validate locally

1. Import project from https://gitlab.com/gitlab-org/govern/threat-insights-demos/verification-projects/438303-limit-vulnerabiility-severity-counts into local and run the pipeline on the main branch. This will populate the vulnerabilities, this project has 1100 vulnerabilities (low: 1045 and critical: 55).
2. Run the GraphQL queries for project.limitedVulnerabilitySeveritycounts, group.limitedVulnerabilitySeveritycounts and instanceSecurityDashboard.limitedVulnerabilitySeveritycounts and we should observe that maximum count returned does not exceed 1001 as shown in screenshots above.

query {
  project(fullPath: "bala-test-group/438303-limit-vulnerabiility-severity-counts") {
    limitedVulnerabilitySeverityCounts(state: [DETECTED]) {
      critical
      high
      info
      low
      medium
      unknown
    }
  }
}

query {
  group(fullPath: "bala-test-group") {
    limitedVulnerabilitySeverityCounts(state: [DETECTED]) {
      critical
      high
      info
      low
      medium
      unknown
    }
  }
}

query {
  instanceSecurityDashboard {
    limitedVulnerabilitySeverityCounts(state: [DETECTED]) {
      critical
      high
      info
      low
      medium
      unknown
    }
  }
}

Related to #438303