Validate installation/linking process is correct

Currently we install librdkafka by bundling it in `inst` and then compiling it as part of the installation. Determine:
1. If there's a way to link to an available installation already if present on the host
2. This works on all 3 major platforms
3. If this is the correct sustainable model. How do we upgrade when new librdkafka versions are released
4. Is this CRAN appropriate