Allow use of non-vendored Zenoh if present (backport #908)

[mergify]

Description

Uses zenoh-c and zenoh-cpp if found by cmake. It's easier to handle distributing and patching of Zenoh on non-standard platforms if the rust build can be handled externally.

Is this user-facing behavior change?

Should not affect any users, unless they are building from source and have installed the libraries to the cmake search path.

Did you use Generative AI?

No

Additional Information

There's also #695 but it seems to have stalled. Would appreciate if this could be considered in the meantime.

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This is an automatic backport of pull request #908 done by Mergify.

[JEnoch]

Pulls: #909
Gist: https://gist.githubusercontent.com/JEnoch/8c6edd9fae8354e202de1a579855475b/raw/2a8f8d366660e4e728dc90f653438c1b0e73ddf4/ros2.repos
BUILD args: "--continue-on-error" --packages-above-and-dependencies zenoh_cpp_vendor zenoh_security_tools rmw_zenoh_cpp
TEST args: --packages-above zenoh_cpp_vendor zenoh_security_tools rmw_zenoh_cpp
ROS Distro: kilted
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/18243

• Linux
• Linux-aarch64
• Linux-rhel
• Windows