feat: [SRTP-1440] Add GPD message k6 stress test

[davideragusi29]

Description

This PR introduces a new k6 performance test targeting the GPD message endpoint and improves the maintainability of the performance testing suite. It adds per-VU authentication token management with automatic refresh to support long-running stress executions and extends shared utilities to standardize payload generation and endpoint configuration. The overall objective is to provide a reliable, reusable, and clearly documented stress test aligned with production-like scenarios.

List of changes

• Added new gpd-message-finder.js k6 performance test
• Added new endpoint configuration:
  • gpdMessage in shared endpoints
• Added generateIuv() utility
• Added generatePositiveLong() utility
• Added buildGpdMessagePayload() payload builder
• Added RTP_CONSUMER credentials mapping
• Extended ACTOR_CREDENTIALS_MAP with RTP_CONSUMER
• Minor cleanup in run-tests.sh removing activation file cleanup block

Motivation and context

A dedicated stress test for the GPD message endpoint was missing, and token handling was not suitable for extended executions, potentially leading to authentication failures. This change ensures stable long-running performance tests by introducing a per-VU token lifecycle strategy and improving code clarity through reusable utilities and documentation.

Aggregation level

• Test case
• Test suite

Test type

• Functional test
• Bdd test
• Performance
• End to end
• Performance

Type of changes

• Add new test case/suite
• Modify existing test case/suite

Test Results

• Success
• Failure
• Poor performance
• [] Good performance

Did you update secrets accordingly?

• Yes
  • .secrets_template.yaml
  • Pipelines' secure file
  • Confluence
• Not needed
• No (please provide further information)

Did you update dependencies accordingly?

• Yes (which requirements.txt did you update?)

• Not needed

Other information