Add error logging to extractor

### What problem are you facing?

When selectors fail to resolve values correctly (see crossplane-contrib/provider-upjet-aws#118), it is hard to diagnose the probable issue.

### How could Upjet help solve your problem?

It would be beneficial to add some additional logging in [extractor.go](https://github.com/crossplane/upjet/blob/1644827c946b45e8087d003b0ae21c8a73bab027/pkg/resource/extractor.go) to log errors, which are currently swallowed silently:
* https://github.com/crossplane/upjet/blob/1644827c946b45e8087d003b0ae21c8a73bab027/pkg/resource/extractor.go#L47-L50
* https://github.com/crossplane/upjet/blob/1644827c946b45e8087d003b0ae21c8a73bab027/pkg/resource/extractor.go#L53-L56