Add DNSSettings for Tracer Configuration (API part)

[aatarasoff]

A new section called dns_settings has been added to the Tracer Configuration. The purpose of this addition is to limit the Istio proxy's DNS queries to 10 minutes instead of the default 30 seconds when Zipkin tracing is enabled. This can be achieved by defining the below structure in MeshConfig using this PR:

dns_settings:
  refresh_rate: "600s"
  respect_ttl: false

Related PR: https://github.com/istio/istio/pull/47049

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• :white_check_mark: login: aatarasoff / name: Aleksandr Tarasov (ccfc94a620d973045b8d28cd1fff046ca5763540)

[istio-testing]

Hi @aatarasoff. Thanks for your PR.

I'm waiting for a istio member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[costinm]

Does this config apply to ALL tracers ? I agree with John, it's something that otel collector should handle.

[hzxuzhonghu]

I think dns refresh rate is not only to tracers, but to all DNS services. We have a DnsRefreshRate in MeshConfig now, but actually we do not allow setting respect_ttl, which is hardcoded to true.

We can add a respect_ttl to meshConfig, and allow agent to get both values

[hzxuzhonghu]

Find that we have also supported dynamic bootstrap discovery, which can be used to customize the whole bootstrap config

[istio-testing]

PR needs rebase.

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