bugfix: S3C-2899 add constants to support versioning key formats
bugfix: S3C-2899 add constants to support versioning key formats

- add constant prefixes for master and version keys

- add versioning key format version numbers

Those constants will be shared between listing logic (in Arsenal) and
put/get/etc. logic (in Metadata), hence needs to be in arsenal.

scality/Arsenal,scality/Arsenal