Add namespace support for topic/service name

[C88-YQ]

🎉 New feature

Related to gazebosim/sdformat#1663

Summary

Add namespace support to entities and apply it to diff drive topics.

Changes:

• Add namespace component
• Add utility helpers to detect whether the ECM contains namespaces and to compute an entity's scoped namespace
  from its parent hierarchy.
• Update DiffDrive to use the scoped namespace when building default command, enable, odometry, and TF topics. Relative custom topic names are prefixed with the scoped namespace, while absolute topic names are left unchanged.

Test it

ctest

Checklist

• Signed all commits for DCO
• Added a screen capture or video to the PR description that demonstrates the feature
• 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)
• Updated Bazel files (if adding new files). Created an issue otherwise.
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