This pull request adds a report on the major bandwidth usage within Tendermint.
[Rendered](https://github.com/tendermint/tendermint/blob/wb/p2p-rfc/docs/rfc/rfc-027-p2p-message-bandwidth-report.md)
#### PR checklist
- [ ] Tests written/updated, or no tests needed
- [ ] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [ ] Updated relevant documentation (`docs/`) and code comments, or no
documentation updates needed