Added error logs in pallet-xcm to help in debugging, fixes #2408 

## TODO

- [x] change `log::error` to `tracing::error` format for `xcm-executor`
- [x] check existing logs, e.g. this one can be extended with more info
`tracing::error!(target: "xcm::reanchor", ?error, "Failed reanchoring
with error");`
- [x] use `tracing` instead of `log` for `pallet-xcm/src/lib.rs`

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Co-authored-by: Ayevbeosa Iyamu <aiyamu@vatebra.com>
Co-authored-by: Adrian Catangiu <adrian@parity.io>
Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: Bastian Köcher <git@kchr.de>