feat: Add total records when fetching records with metadata filter

[frascuchon]

Description

This PR includes the total number of records when some metadata filter is applied for endpoints /api/v1/me/datasets/:dataset_id/records and /api/v1/datasets/:dataset_id/records

In the future, this value will be computed for all cases and not only when metadata_filter is applied

Type of change

(Please delete options that are not relevant. Remember to title the PR according to the type of change)

• New feature (non-breaking change which adds functionality)
• Refactor (change restructuring the codebase without changing functionality)
• Improvement (change adding some improvement to an existing functionality)

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I filled out the contributor form (see text above)
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)