test: add dns-loop (actually curl) stress test

[jackfrancis]

Reason for Change:

This PR adds a simple, one-time stress test to validate that a bunch of curls to a well-known external URL are responsive.

Nominally these checks actually do a curl, which relies upon the entire HTTP stack, but in practice they will surface high DNS lookups, which we've observed in the past.

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[jackfrancis]

cc @alexeldeib

and thx again @sturrent!

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

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[codecov]

Codecov Report

Merging #4024 (f29a344) into master (e780eeb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4024   +/-   ##
=======================================
  Coverage   73.69%   73.69%           
=======================================
  Files         147      147           
  Lines       23164    23164           
=======================================
  Hits        17070    17070           
  Misses       4979     4979           
  Partials     1115     1115           

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