Build refactoring - cbindgen (#313)

* Build refactoring - cbindgen
Ensure cbindgen is included in the package's build steps.
The motivation is to remove logic from the shell scripts.

* Cbindgen refactor - Adjust 3rd party license file

* cbindgen refactoring - minor rerun policy update
Ensure we re-run cargo build scripts if cbindgen.toml file is udpated

* cbindgen build step - refactor
Add a function to read configuration from env vars
and calls into the header generation functions.

* cbindgen through cargo build scripts - Path resolution improvement

When DESTDIR is set, ensure we use the cargo target path to compute absolute paths.

* cbindgen generation through build scripts - Improve management of relative paths

Use the locate-project feature to find the root of the project.

* Minor clippy fix

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Co-authored-by: Daniel Schwartz-Narbonne <daniel.schwartznarbonne@datadoghq.com>

.gitignore

@@ -7,7 +7,7 @@
 .idea
 .vs
 .vscode
-build*/
+build/
 cmake-build-debug
 deliverables
 target