Set seed value using CLI

[adityapande-1995]

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🎉 New feature

Closes #1467

Summary

This PR exposes a --seed argument to gz sim to set seed value for the random number generator.

Test it

Added a small test case that runs gz sim -s -v 4 --seed 5 --iterations 5 and checks for the output string "Setting seed value: 5" in stdout.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• 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.

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[chapulina]

LGTM so far, just pending a test

[chapulina]

Removed the Garden label because we're past feature freeze ❄️ .

This PR can either be merged into main and backported to gz-sim7 after the stable release, or retargeted to gz-sim7 and merged after the stable release (i.e. October).

[adityapande-1995]

The CI failures here seem unrelated to the changes made here.