SYN-4475: Adds chrome flags to provider

[sangn-splunk]

Resolves SYN-4475

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Before the change?

• Browser configs do not support chrome_flags.

After the change?

• Browser configs should support chrome_flags.

Pull request checklist

• Acceptance Tests have been updated, run (make testacc), and pasted in this PR (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Acceptance Test Output

$ TF_ACC=1 TF_LOG=INFO go test ./synthetics/... -run TestAccCreateUpdateBrowserCheckV2
ok      github.com/splunk/terraform-provider-synthetics/synthetics      (cached)

Does this introduce a breaking change?

• Yes
• No

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