Backport of Include RequestTimeout in marshal/unmarshal of ServiceResolverConfigE… into release/1.15.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #19031 to be assessed for backporting due to the inclusion of the label backport/1.15.

The below text is copied from the body of the original PR.

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Description

This PR fixes a bug where we’re missing the custom JSON marshal and unmarshal for the ServiceResolverConfigEntry.RequestTimeout field. This has the effect that the config entry can be written successfully to Consul but it cannot be read back through the API.

Testing & Reproduction steps

Before the changes proposed in this PR:

$ consul agent -dev &> /dev/null &
$ consul config write -
Kind      = "service-resolver"
Name      = "frontend-se"
ConnectTimeout = "10s"
RequestTimeout = "15s"
Subsets = {
 v1 = {
   OnlyPassing = true
 }
 v2  = {
   OnlyPassing = true
 }
}^D
Config entry written: service-resolver/frontend-se
$ consul config read -kind service-resolver -name frontend-se
Error reading config entry service-resolver/frontend-se: json: cannot unmarshal string into Go struct field .RequestTimeout of type time.Duration

After these changes:

# setup as above
consul config read -kind service-resolver -name frontend-se
{
    "ConnectTimeout": "10s",
    "RequestTimeout": "15s",
    "Kind": "service-resolver",
    "Name": "frontend-se",
    "Partition": "default",
    "Namespace": "default",
    "Subsets": {
        "v1": {
            "OnlyPassing": true
        },
        "v2": {
            "OnlyPassing": true
        }
    },
    "CreateIndex": 22,
    "ModifyIndex": 22
}

PR Checklist

• updated test coverage
• external facing docs updated
• appropriate backport labels added
• not a security concern

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Overview of commits

• 4ad1a87 - 9109bdd

[github-team-consul-core-pr-approver]

Auto approved Consul Bot automated PR

[hc-github-team-consul-core]

🤔 This PR has changes in the website/ directory but does not have a type/docs-cherrypick label. If the changes are for the next version, this can be ignored. If they are updates to current docs, attach the label to auto cherrypick to the stable-website branch after merging.