Use exec instead of popen to run CLI11 based binaries

[azeey]

🦟 Bug fix

Summary

See gazebosim/gz-launch#151

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• 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 #300 (7ac5409) into ign-transport10 (4daffb6) will not change coverage.
The diff coverage is n/a.

❗ Current head 7ac5409 differs from pull request most recent head 32ea3ce. Consider uploading reports for the commit 32ea3ce to get more accurate results

@@               Coverage Diff                @@
##           ign-transport10     #300   +/-   ##
================================================
  Coverage            89.09%   89.09%           
================================================
  Files                   51       51           
  Lines                 4777     4777           
================================================
  Hits                  4256     4256           
  Misses                 521      521           

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[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-03-25-fortress-edifice-citadel/1343/1