[GCP] Refactor `RunPingConnectivityTest`

[seankimkdy]

Changed the arguments of RunPingConnectivityTest such that users don't need to pass in networkmanagement.networkmanagementpb.Endpoints. This is an exported function meant to be used in functional tests, so I presumed a new list of arguments with IP addresses and namespaces is better than using a specific GCP API struct.

Also fixes #158. Helps maintain consistency in how we export methods.

[github-actions[bot]]

Unit Test Results

302 tests  ±0   302 :white_check_mark: ±0   2s :stopwatch: -3s  48 suites ±0     0 :zzz: ±0    1 files   ±0     0 :x: ±0 

Results for commit e3b52a9d. ± Comparison against base commit e9e67cad.

[github-actions[bot]]

For the detailed report, please go to Checks tab, click Build and Test, and then download unit_test_coverage artifact at the bottom of build page.

• Your PR branch coverage: 50.5 %
• main branch coverage: 0 %
• diff coverage: 50.5 %

The coverage result does not include the functional test results.