SYN-6813: add GetChromeFlags() to fetch chrome_flags endpoint

[jcsco]

Summary

• Adds GetChromeFlags() in syntheticsclientv2 that calls GET /chrome_flags and returns the existing ChromeFlagsResponse struct (previously dead code), following the GetExcludedFileTypesV2 single-GET pattern.
• Adds unit tests covering the happy path, malformed JSON response, and network failure.

This is a prerequisite for wiring up a synthetics_chrome_flags data source in terraform-provider-synthetics (SYN-6813), which will land once this client change is released.

Test plan

• go test ./syntheticsclientv2/... -run ChromeFlags -v passes
• go build ./... and go vet ./... clean

Jira: https://splunk.atlassian.net/browse/SYN-6813

[github-actions]

Code Coverage Report:

Total coverage threshold (90%) satisfied:	PASS
Total test coverage: 94.5% (942/997)

No coverage changes in any files compared to the base.

[github-actions]

Integration Test: ✅ Passed

View run

Live integration tests — Total: 60 | Passed: 60 | Failed: 0 | Skipped: 0

Test	Result	Duration (s)
TestLiveApiCheckCreateUpdateAndDeleteV2	✅ Pass	1.58
TestLiveBrowserCheckCreateUpdateAndDeleteV2	✅ Pass	1.82
TestLiveCaCertificateCreateUpdateAndDeleteV2	✅ Pass	1.26
TestLiveClientCertificateCreateUpdateAndDeleteV2	✅ Pass	1.28
TestLiveCreateApiCheckV2	✅ Pass	0.52
TestLiveCreateBrowserCheckV2	✅ Pass	0.61
TestLiveCreateCaCertificateV2	✅ Pass	0.51
TestLiveCreateClientCertificateV2	✅ Pass	0.54
TestLiveCreateHttpCheckV2	✅ Pass	0.54
TestLiveCreateLocationV2	✅ Pass	0.49
TestLiveCreatePortCheckV2	✅ Pass	0.5
TestLiveCreateSslCheckV2	✅ Pass	0.52
TestLiveCreateTotpVariableV2	✅ Pass	0.49
TestLiveCreateVariableV2	✅ Pass	0.55
TestLiveCreateVariableV2ReturnsErrorOnDuplicateName	✅ Pass	0.68
TestLiveDeleteApiCheckV2	✅ Pass	0.51
TestLiveDeleteApiCheckV2ReturnsErrorForNonexistentID	✅ Pass	0.22
TestLiveDeleteBrowserCheckV2	✅ Pass	0.5
TestLiveDeleteCaCertificateV2	✅ Pass	0.51
TestLiveDeleteClientCertificateV2	✅ Pass	0.51
TestLiveDeleteHttpCheckV2	✅ Pass	0.65
TestLiveDeleteLocationV2	✅ Pass	0.47
TestLiveDeletePortCheckV2	✅ Pass	0.54
TestLiveDeleteSslCheckV2	✅ Pass	0.52
TestLiveDeleteTotpVariableV2	✅ Pass	0.49
TestLiveDeleteVariableV2	✅ Pass	0.62
TestLiveDowntimeConfigurationCreateUpdateAndDeleteV2	✅ Pass	1.77
TestLiveGetApiCheckV2	✅ Pass	0.86
TestLiveGetBrowserCheckV2	✅ Pass	0.75
TestLiveGetCaCertificateV2	✅ Pass	0.72
TestLiveGetChecksV2	✅ Pass	0.67
TestLiveGetChromeFlags	✅ Pass	0.22
TestLiveGetClientCertificateV2	✅ Pass	0.79
TestLiveGetDevicesV2	✅ Pass	0.23
TestLiveGetDowntimeConfigurationsV2	✅ Pass	1.39
TestLiveGetExcludedFileTypesV2	✅ Pass	0.22
TestLiveGetHttpCheckV2	✅ Pass	0.76
TestLiveGetHttpCheckV2ReturnsErrorForNonexistentID	✅ Pass	0.22
TestLiveGetLocationsV2	✅ Pass	0.22
TestLiveGetLocationV2	✅ Pass	0.22
TestLiveGetPortCheckV2	✅ Pass	0.74
TestLiveGetSslCheckV2	✅ Pass	0.87
TestLiveGetTotpVariableV2	✅ Pass	0.7
TestLiveGetVariablesV2	✅ Pass	0.71
TestLiveGetVariableV2	✅ Pass	0.71
TestLiveGetVariableV2ReturnsErrorForNonexistentID	✅ Pass	0.22
TestLiveHttpCheckCreateUpdateDeleteV2	✅ Pass	1.93
TestLiveHttpCheckWithNullablePortCreateUpdateAndDeleteV2	✅ Pass	1.04
TestLivePortCheckCreateUpdateAndDeleteV2	✅ Pass	1.47
TestLiveSslCheckCreateUpdateAndDeleteV2	✅ Pass	1.07
TestLiveTotpVariableCreateUpdateAndDeleteV2	✅ Pass	1.17
TestLiveUpdateApiCheckV2	✅ Pass	0.82
TestLiveUpdateBrowserCheckV2	✅ Pass	0.84
TestLiveUpdateCaCertificateV2	✅ Pass	0.98
TestLiveUpdateClientCertificateV2	✅ Pass	0.95
TestLiveUpdateHttpCheckV2	✅ Pass	0.82
TestLiveUpdatePortCheckV2	✅ Pass	0.76
TestLiveUpdateSslCheckV2	✅ Pass	1
TestLiveUpdateTotpVariableV2	✅ Pass	0.91
TestLiveUpdateVariableV2	✅ Pass	0.82