fix(build): Add libevent-dev dependency

[ananos]

What does the PR do?

libevent-dev is needed for building the server from source.

Checklist

• I have read the Contribution guidelines and signed the Contributor License
  Agreement
• PR title reflects the change and is of format <commit_type>: <Title>
• Changes are described in the pull request.
• Related issues are referenced.
• Populated github labels field
• Added test plan and verified test passes.
• Verified that the PR passes existing CI.
• I ran pre-commit locally (pre-commit install, pre-commit run --all)
• Verified copyright is correct on all changed files.
• Added succinct git squash message before merging ref.
• All template sections are filled out.
• Optional: Additional screenshots for behavior/output changes with before/after.

Commit Type:

Check the conventional commit type
box here and add the label to the github PR.

• build
• ci
• docs
• feat
• fix
• perf
• refactor
• revert
• style
• test

Related PRs:

Where should the reviewer start?

Test plan:

Caveats:

Background

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)

• closes GitHub issue: Build error when trying to build cpu only version of nvidia triton server #8513

[whoisj]

@ananos, thank you for your contribution. Have you already completed our contribution requirements?

https://github.com/triton-inference-server/server?tab=readme-ov-file#contributing

@mc-nv to review.

[mc-nv]

@ananos, thank you for your contribution. Have you already completed our contribution requirements?

https://github.com/triton-inference-server/server?tab=readme-ov-file#contributing

@mc-nv to review.

As you can see we are using third_party references for libevent.
https://github.com/triton-inference-server/server/blob/main/CMakeLists.txt#L225

This change will lead us to the many other similar changes.
We can accept this change but it requires following changes as well.
Eliminating unused code in CMake repository.
https://github.com/triton-inference-server/third_party/blob/84a6bacf4f2982024d1466485e89cb29b8925b6a/CMakeLists.txt#L296-L310

once it done we need to reevaluate and confirm that everything can be built correctly.

I would like to defer it to @dzier for prioritization, with a comment that it's related to the effort we been talking for years with dependency management implementation.