docs: multiregion deployment feature

[tgross]

To go with #8184

[angrycub]

saw an &emdash; leaking out to the output. Not sure how to fix yet or would have made a suggestion. Just wanted to let you know I was looking.

[tgross]

Fixed the emdash in 89eca7f

[tgross]

@yishan-lin @changli0617 it'd probably be worth getting some of your input here with respect to the nomenclature gap between "Multi-Cluster Deployment" and "multiregion deployment" as it's been crafted in the implementation. The operator-facing concept in Nomad is the region (see also region and the Multi-Region Federation Guide), which is why we used the configuration value multiregion.

It's probably fine that we have the "marketing name" in the enterprise section of the docs here so long as it points to the operator-facing name, but I wanted to bring it to your attention.

[schmichael]

Looks good! re Multi-cluster vs Multiregion:

We'll have to live with some ambiguity unfortunately, but I think it's for good reason:

1. "Multi-cluster" will be used in marketing material where the audience may not be familiar with Nomad's notion of "regions"
2. "Multiregion" will be used in reference material as it uses Nomad-specific terminology

Since Nomad "clusters" and "regions" are synonymous, hopefully using both terms isn't too jarring. If so we may make changes to marketing material over time, but the technical implementation (and therefore reference docs too) would continue to use the Nomad-specific terminology.

[tgross]

Previews:

• https://deploy-preview-8185--nomad-website.netlify.app/docs/job-specification/multiregion/
• https://deploy-preview-8185--nomad-website.netlify.app/docs/enterprise/#multi-cluster-efficiency
• https://deploy-preview-8185--nomad-website.netlify.app/docs/commands/deployment/unblock/

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