borg2: match on username, hostname, tags, ...

[ThomasWaldmann]

matching of archives in borg has historically been focussed on the archive name, because everything was put into there in borg 1.x:

• the timestamp was put into the name to make it unique
• other stuff was put into the name, because there was no other place to put it (besides the comment) and also because borg list only showed name, timestamp, id.

borg2 now started to clean this up:

• name does not need to be unique anymore, thus no need to put the timestamp into the name.
• by having the same names for all archives in a series, some stuff got easier (finding previous archive, files cache separation, pruning, operating on all archives of a series)

but while implementing #8422 i noticed that we currently can still only use name matching for borg prune (either precise or wildcard match).

we can not yet match on the username or hostname, so users would still need to put these into the archive name if they want to treat different user's/hosts' stuff separately by prune.

to improve that, we need "and"-matching for:

• archive name (exists)
• user name
• host name
• tags

So we can then say something like:

borg prune name:home user:tw host:server --keep-daily 30
borg prune name:home user:gw host:server --keep-daily 30