storage controller: validate DNS of registering nodes

[jcsp]

Problem

A node with a bad DNS configuration can register itself with the storage controller, and the controller will try and schedule work onto the node, but never succeed because it can't reach the node.

The DNS case is a special case of asymmetric network issues. The general case isn't covered here -- but might make sense to tighten up after #6844 merges -- then we can avoid assuming a node is immediately available in re_attach.

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2520 tests run: 2395 passed, 0 failed, 125 skipped (full report)

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Code coverage* (full report)

• functions: 28.7% (7028 of 24494 functions)
• lines: 47.4% (43418 of 91518 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
b27935e at 2024-03-13T10:32:55.627Z :recycle:}