Configure DNS refresh rate from DNS record TTL

[Alice-Lilith]

Signed-off-by: AliceProxy [email protected]

Description

Creates a new field in Mappings called respect_dns_ttl this configures Envoy’s DNS refresh rate for the Mapping. When true, the cluster’s DNS refresh rate will be set to resource record’s TTL which comes from DNS resolution.

Relevant Envoy Config

Related Issues

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Testing

A few sentences describing what testing you've done, e.g., manual tests, automated tests, deployed in production, etc.

Checklist

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• I updated DEVELOPING.md with any any special dev tricks I had to use to work on this code efficiently.

[kflynn]

I'm honestly debating whether we should make this the default...

[kflynn]

Looks good except for the lack of a CHANGELOG entry. I'm going to merge this one anyway, and will follow up on the CHANGELOG separately.