Backport of Add Nomad RetryConfig to agent template config into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #13907 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

WARNING automatic cherry-pick of commits failed. Commits will require human attention.

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

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Closes #13019

This PR introduces a retry configuration option for Nomad dependencies in Consul Template. For example, Nomad native service discovery and secure variables will make calls to the Nomad API. If connectivity is lost between the client and the servers, these calls will fail and the task may fail or run with stale data forever depending on the type of error. Operators can now specify a nomad_retry stanza in the same way they can for Vault or Consul. The default config attempts is set to 0 which allows for infinite retries.

[hashicorp-cla]

All committers have signed the CLA.

[DerekStrickland]

I think this is G2G. Waiting for @lgfa29 to concur.

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