feat(anta): Added the test case to verify the Graceful Restart (GR) and GR-Helper

[geetanjalimanegslab]

Description

This test performs the following checks:

 1. Verifies that the ISIS is configured.
 2. Verifies that the specified VRF is found.
 3. Verifies that the specified VRF instance is found.
 4. Verifies that the IS-IS graceful restart and graceful helper are set as expected in the inputs.

Expected Results
----------------
* Success: The test will pass if graceful restart and graceful helper are set as expected for a specified VRF instance.
* Failure: The test will fail if graceful restart and graceful helper are not set as expected for a specified VRF instance.

Fixes #882

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have run pre-commit for code linting and typing (pre-commit run)
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes (tox -e testenv)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codspeed-hq]

CodSpeed Performance Report

Merging #988 will not alter performance

_{Comparing geetanjalimanegslab:test_isis_graceful_restart (f2eb754) with main (2a0bf6c)}

Summary

✅ 22 untouched benchmarks