Add role update functionality to acl token update

[Kartik1397]

This pull request adds the ability to update roles in the acl token update command.

Fixes: #18354

[hashicorp-cla]

All committers have signed the CLA.

[lgfa29]

Looking good @Kartik1397, thank you for the PR! I left a suggestion about how to handle the removal of roles from a token.

Would you also be able to update the documentation page to include these new flags?
https://github.com/hashicorp/nomad/blob/main/website/content/docs/commands/acl/token/update.mdx

And also run the command make cl to generate a CHANGELOG entry.

Thanks again for the contribution!

[tgross]

I've rebased this PR on main, pushed a changelog entry, resolved the open comments, and added documentation updates. Will merge once this is green and that'll ship in Nomad 1.8.3.

[github-actions]

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