This change better resembles the output generated by `Snapshot.String()`,
which includes both username and hostname.
Closes #4506
Before:
```
$ restic copy --from-repo /srv/restic-repo
repository 3666882b opened (version 2, compression level auto)
repository 0085c387 opened (version 2, compression level auto)
created new cache in /home/mike/.cache/restic
[0:00] 100.00% 1 / 1 index files loaded
[0:00] 0 index files loaded
snapshot 32b39a20 of [/home/mike/data] at 2023-10-21 16:01:13.979948154 -0300 -03)
copy started, this may take a while...
[0:00] 100.00% 1 / 1 packs copied
snapshot 10331fdd saved
```
After:
```
$ restic copy --from-repo /srv/restic-repo
repository 3666882b opened (version 2, compression level auto)
repository 0085c387 opened (version 2, compression level auto)
[0:00] 100.00% 1 / 1 index files loaded
[0:00] 0 index files loaded
snapshot 32b39a20 of [/home/mike/data] at 2023-10-21 16:01:13.979948154 -0300 -03 by mike@desktop)
copy started, this may take a while...
[0:00] 100.00% 1 / 1 packs copied
snapshot a67bd1ee saved
```
The previous approach of rewriting all snapshots first, then flushing
the repository data and finally removing old snapshots has the downside
that an interrupted command execution leaves behind broken snapshots as
not all new data is already flushed.
The files in a tree must be sorted in lexical order. However, this
cannot be guaranteed when appending a filename suffix. For two files
file, file.rep
where "file" is broken, this would result in
file.repaired, file.rep
which is no longer sorted.
In addition, adding a filename suffix is also prone to filename
collisions which would require a rather complex search for a
collision-free name in order to work reliably.
Simplify CLI options:
* Rename "DeleteSnapshots" to "Forget"
* Replace "AddTag" and "Append" with hardcoded values
Change output and snapshot modifications to be more in line with the
"rewrite" command.
