Allow schema collectors to customize count metric name

[mobuchowski]

What does this PR do?

Adds an overridable object_count_metric_name property to the shared schema collector. Existing collectors retain dd.<dbms>.schema.tables_count by default, while specialized collectors can report a distinct object-count metric.

Motivation

The SQL Server view collector reuses the shared schema collection lifecycle but must report views_count without submitting view rows to the existing table-count metric.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add qa/required if this PR needs QA validation, or qa/skip-qa if it does not. Exactly one of the two is required.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[cit-pr-commenter-54b7da]

evalya-impact-summary

evalya impact analysis

Impact analysis: 0 selected, 0 skipped (of 0 test tasks)
Publish tasks:   1 (always emitted)
Diff (2 files):
  datadog_checks_base/changelog.d/24947.fixed
  datadog_checks_base/datadog_checks/base/utils/db/schemas.py

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[datadog-prod-us1-3]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 88.75%

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[dd-octo-sts]

Validation Report

All 21 validations passed.

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jmx-metrics	Validate JMX metrics definition files and config	✅
labeler	Validate PR labeler config matches integration directories	✅
legacy-signature	Validate no integration uses the legacy Agent check signature	✅
license-headers	Validate Python files have proper license headers	✅
licenses	Validate third-party license attribution list	✅
metadata	Validate metadata.csv metric definitions	✅
models	Validate configuration data models match spec.yaml	✅
openmetrics	Validate OpenMetrics integrations disable the metric limit	✅
package	Validate Python package metadata and naming	✅
qa-label	Validate the pull request declares whether it needs QA for the next Agent release	✅
readmes	Validate README files have required sections	✅
saved-views	Validate saved view JSON file structure and fields	✅
version	Validate version consistency between package and changelog	✅

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