Backport of parse ACL token from authorization header into release/1.3.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #12534 to be assessed for backporting due to the inclusion of the label backport/1.3.x.

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

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Adds support for reading ACL token from the RFC6750 Bearer token (Authorization: Bearer <token>).

The code samples / documentation were taken from Consul:
https://github.com/hashicorp/consul/blob/973d2d0f9a2d32f6f3eae506c2b5b89f98007b58/agent/http.go#L1021-L1041
https://github.com/hashicorp/consul/blob/1d817f683a4922756db44b991428cd5f582ea6ae/website/content/api-docs/index.mdx

Background behind this is I'm using prometheus static_config to scrape metrics from nomad and the static_config configuration doesn't support custom headers, only authorization tokens. This would allow me to properly embed and use the token.

I have yet to test the locally, but will update here when I have a chance to do. Wanted to start the conversation of if this is something y'all wanted to support.

Let me know your thoughts and if there is anything else I should add!

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