Include trailing slash in /computer/xxx/ links

[jglick]

Otherwise org.kohsuke.stapler.DirectoryishDispatcher has to serve a 302 to the correct URL, which is wasteful.

Testing done

Interactive testing with mock-agent used from both freestyle and Pipeline jobs in various views.

Proposed changelog entries

N/A (too minor?)

Proposed upgrade guidelines

N/A

Desired reviewers

@Vlatombe

Before the changes are marked as ready-for-merge:

Maintainer checklist

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1. There are at least two (2) approvals for the pull request and no outstanding requests for change.
2. Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
3. Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
4. Proper changelog labels are set so that the changelog can be generated automatically.
5. If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
6. If it would make sense to backport the change to LTS, a Jira issue must exist, be a Bug or Improvement, and be labeled as lts-candidate to be considered (see query).