Add missing config.hh include to gz headers

[scpeters]

🦟 Bug fix

Fixes some gz headers

Summary

The gz/utils/*.hh headers on ign-utils1 that use the ignition namespace need to include gz/utils/config.hh to get the gz namespace. I found this while trying to use gz::utils::ImplPtr in sdformat12:

• https://github.com/gazebosim/sdformat/actions/runs/3681027316/jobs/6227265470#step:8:88

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #90 (5a2174e) into ign-utils1 (64765dc) will not change coverage.
The diff coverage is n/a.

❗ Current head 5a2174e differs from pull request most recent head dfcc3d4. Consider uploading reports for the commit dfcc3d4 to get more accurate results

@@             Coverage Diff             @@
##           ign-utils1      #90   +/-   ##
===========================================
  Coverage       91.97%   91.97%           
===========================================
  Files               6        6           
  Lines             137      137           
===========================================
  Hits              126      126           
  Misses             11       11           

Impacted Files	Coverage Δ
include/gz/utils/ImplPtr.hh	100.00% <ø> (ø)
include/gz/utils/NeverDestroyed.hh	100.00% <ø> (ø)

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