archive(1.3) exclusion: remove versions 1.3 and 3.7.0, part 1: reviewable steps

[pepopowitz]

DO NOT MERGE until #4474 has been published to the standalone 1.3 site.

Description

Part of #2189.

Includes the smaller items for removing version 1.3/3.7.0 from the main docs, to keep the PR in a reviewable state.

Included in this PR

• Remove v1.3 & Optimize v3.7.0 from the version manifest files, so that they're not included in the deployed site
• Redirect all 1.3 / 3.7.0 traffic to unsupported.docs.camunda.io/1.3 (or stage.unsupported.docs.camunda.io/1.3 for the staging build)
• Move "1.3 / 3.7.0" versions to the "Unsupported versions" sub-list in the top nav version selector, redirecting to unsupported.docs.camunda.io/1.3.
• Remove v1.3 & Optimize v3.7.0 from the sitemap ignore patterns.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.

• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

• My changes require a docs infrastructure review.