Mercurial changesets can contain [[ https://www.mercurial-scm.org/wiki/ChangesetExtra | extra data ]] in it.
Notably, the `transplant_source` changeset extra contain a [[ https://www.mercurial-scm.org/wiki/Nodeid | nodeid ]] in binary format.
We should convert that nodeid into its hexadecimal representation before adding it to a swh revision metadata in order to avoid
`UnicodeDecodeError` when one wants to decode the collected metadata to `utf-8`.
Related T1727