Postgres model bulk save, Redis model mget

Co tenhle MR dělá? / What does this MR do?

Added

• PostgresModel - bulkSave method to properly upsert multiple records at once
• RedisModel - mget method to retrieve multiple values at once

Související issues / Related issues

Prepis bulkUpdate/bulkUpsert interne používajúc... (pid#302 - closed)

Vývojářův kontrolní seznam / Developer checklist

• Ensure this change works
• Write unit tests for this change as needed
• Update the OpenAPI document if exists
• Ensure CI/CD pipeline passes
• Create or update the implementation documentation if necessary
• Include a changelog entry
• Request a review

Recenzentův kontrolní seznam / Reviewer checklist

• Ensure this change follows CODING-GUIDELINES and CONTRIBUTING
• Ensure this change follows the Golemio/OICT architecture
• Ensure this change does not add unnecessary dependencies (e.g. lodash)
• The changelog is updated
• The implementation documentation is created or updated if necessary
• The OpenAPI document is updated if exists