Support uploading client ACL tokens

[allisonlarson]

Description

Adds support for uploading client ACL tokens by supplying the accessorID and secretID during creation. The command nomad acl token create now takes an optional -accessor flag, and the secretID is provided either by a filepath or through stdin (-), following how nomad acl bootstrap accepts the secretID. If the accessor is provided, the secretID is required; similarly, if the secretID is passed, the accessor is required. Management tokens are not allowed to be uploaded in this way.

I've added a new ACLTokens.Upload function to the api package for clarity and clear validation message, but it still uses the same http path & requests. I can collapse this into the same ACLTokens.Create, but the specificity felt nicer.

Testing & Reproduction steps

tests were added, and tested manually

Links

Issue: #24457
Internal ref: https://hashicorp.atlassian.net/browse/NMD-352

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Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.