Backport of Allocation API: fix "no path to region" errors for non-global regions into release/1.9.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #24644 to be assessed for backporting due to the inclusion of the label backport/1.9.x.

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

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In #16872 we added support for unix domain sockets, but this required mutating the Config when parsing the address so as to remove the port number. In #23785 we fixed a bug where if the configuration was used across multiple clients (as in the autoscaler) that mutation would happen multiple times and the address would be incorrectly parsed.

When making alloc log, alloc fs, or alloc exec calls where we have line-of-sight to the client, we attempt to make a HTTP API call directly to the client node. So we create a new API client from the same configuration and then set the address. But in this case we copy the private url field and that causes the URL parsing to be skipped for the new client.

This results in the region always being set to the string literal "global" (because of mTLS handling code introduced all the way back in 4d3b75d), unless the user has set the region specifically. This fails with an error "no path to region" when the cluster isn't non-global and requests are sent to a non-leader.

Arguably the "right" way of fixing this would be for ClientConfig not to change the API client's region to "global" in the first place, but as this is a public API and extremely longstanding behavior, it could potentially be a breaking change for some downstream consumers. Instead, we'll avoid copying the private url field so that the new address is re-parsed.

Fixes: #24635
Fixes: #24609
Ref: #16872
Ref: #23785
Ref: 4d3b75d
Ref: https://hashicorp.atlassian.net/browse/NET-11858

Testing & Reproduction steps

To reproduce, stand up a cluster with region = "example" with at least one client, in an environment where you have line-of-sight to all nodes (ex. local development environment should work fine). Deploy a job to that client and run nomad alloc logs :alloc_id.

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Overview of commits

• 75b0202

[hashicorp-cla-app]

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[tgross]

Fixed backport. Will need re-review.

had to fix