CONTRIBUTING - update PR with example of new project

[Kielek]

Replaces #2919, I needed to make hard cleanup in my fork after some tests

Changes

CONTRIBUTING - update PR with example of new project
the previous one is outdated

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• [ ] Unit tests added/updated
• [ ] Appropriate CHANGELOG.md files updated for non-trivial changes
• [ ] Changes in public API reviewed (if applicable)

[thompson-tomo]

I would call that a bad example as the build consumes over 6hrs of build time & runs over 200 actions hence not efficient. I wouldn't want more projects following that example, hence a better example should be selected.

[Kielek]

It is about document current state of the implementation. If you see possibility to improve, we are opened for this.
If changes are touch only one project, only small subset of builds is executed. See: https://github.com/open-telemetry/opentelemetry-dotnet-contrib/blob/main/.github/workflows/ci.yml#L25-L74

[thompson-tomo]

i am aware of that massive if etc. If you look at: #2926 you will see what i am seeing as that did a massive run and we are yet to see a case of a non massive run. The only change to a file not in the opamp folder is the removal of a project from the verify-aot step but it still ran a massive long list of actions hence far from efficent. It appears to be simply treating any yaml changes in the github folder as grounds for an entire build, hence lots of room for improvement. I have already put in a PR to adopt modules which detangles responsibility for build process and is all documented.