Backport of agent: add disable_keep_alives configurable into release/1.11.x

[hc-github-team-secure-vault-core]

Backport

This PR is auto-generated from #16479 to be assessed for backporting due to the inclusion of the label backport/1.11.x.

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

---

Follow up for #15986.

This PR adds a new configurable, disable_keep_alives, which takes a string list to disable keep alives for various features in Vault Agent (auto-auth, caching and templating).

A small example can be found here:

 "auto_auth" = {
  "method" = {
    "config" = {
      "role" = "app"
    }
    "type" = "kubernetes"
  }

  "sink" = {
    "config" = {
      "path" = "/home/vault/.token"
    }
    "type" = "file"
  }
}

"disable_idle_connections" = ["auto-auth", "caching", "templating"]
"disable_keep_alives" = ["auto-auth", "caching", "templating"]
"exit_after_auth" = false
"pid_file" = "/home/vault/.pid"

"template" = {
  "contents" = "{{ with secret \"secret/hashiconf\" }}{{ .Data | toJSONPretty }}{{ end }}"
  "destination" = "/vault/secrets/kv-secret"
  "error_on_missing_key" = true
}

"vault" = {
  "address" = "https://vault.vault.svc.cluster.local:8200"
}

---

Overview of commits

• 4bcc7e1