feat(synthetics): add next gen runtime support to step, cert check, broken links monitors

[pranav-new-relic]

This PR aims at

• adding code changes to step, cert check and broken links monitors to support the next gen runtime (runtime type CHROME_BROWSER and version 100 for step monitors; runtime type NODE_API and version 16.10 for broken links and cert check monitors)
• updates to tests for the same

All changes have been tested manually as well.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 12.78195% with 232 lines in your changes are missing coverage. Please review.

Project coverage is 33.69%. Comparing base (b0bdc28) to head (d50c0bf).

Files	Patch %	Lines
...resource_newrelic_synthetics_cert_check_monitor.go	11.23%	79 Missing :warning:
...ctures_newrelic_synthetics_broken_links_monitor.go	0.00%	36 Missing :warning:
...lic/structures_newrelic_synthetics_step_monitor.go	0.00%	36 Missing :warning:
...source_newrelic_synthetics_broken_links_monitor.go	3.03%	32 Missing :warning:
...relic/resource_newrelic_synthetics_step_monitor.go	23.80%	32 Missing :warning:
newrelic/resource_helpers_synthetics.go	43.33%	17 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2602 +/- ## ========================================== + Coverage 33.01% 33.69% +0.68% ========================================== Files 98 98 Lines 26623 26871 +248 ========================================== + Hits 8790 9055 +265 + Misses 17675 17622 -53 - Partials 158 194 +36 ```

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[pranav-new-relic]

(March 26, 2024)