Enable libcnb tracing (#208)

This enables `libcnb`'s `trace` feature, which means traces, spans, and
events are written to OpenTelemetry export files on disk in the ephemeral
build container, which can then be read by the Heroku build system or
when debugging locally with Pack (so long as a suitable `--volume` mount
has been configured).

See:
heroku/libcnb.rs#723

GUS-W-15108954.

CHANGELOG.md

@@ -7,9 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Enabled tracing/telemetry via `libcnb`'s `trace` feature. ([#208](https://github.com/heroku/procfile-cnb/pull/208))
+
 ### Changed
 
-- Update to Buildpack API 0.10. ([#205](https://github.com/heroku/procfile-cnb/pull/205)
+- Updated to Buildpack API 0.10. ([#205](https://github.com/heroku/procfile-cnb/pull/205))
     - All launch processes are now wrapped in `bash -c` instead of using CNB's `direct = false` directive, which is no longer available.
     - `.profile` and `.profile.d` scripts will no longer be automatically sourced.
     - CNB Lifecycle 0.17 or newer is now required.