Add archive metadata support to eoscta

Task

HTTP archive requests will include a special ArchiveMetadata header for archive metadata, as a JSON encoded in base64 format.

This field will eventually need to be passed down to CTA.
For the moment, we only need to receive and log it's contento in the EOS report logs.

References

CTA ops issue:

• https://gitlab.cern.ch/cta/operations/-/issues/1374

Gfal2 Jira issue:

• https://its.cern.ch/jira/browse/DMC-1409