shell: expand ~ in local file path arguments (#9265)

* shell: expand `~` in local file path arguments

The weed shell parses commands itself instead of going through an OS
shell, so a path like `~/Downloads/foo.meta` was passed verbatim to
`os.Open`, which fails because no `~` directory exists. Users had to
spell out absolute home paths in every command.

Add an `expandHomeDir` helper that resolves a leading `~` or `~/...` to
the user's home directory, and run user-supplied local file paths in
the affected shell commands through it:

  fs.meta.load          (positional file)
  fs.meta.save          (-o)
  fs.meta.changeVolumeId (-mapping)
  s3.iam.export         (-file)
  s3.iam.import         (-file)
  s3.policy             (-file)
  s3tables.bucket       (-file)
  s3tables.table        (-file, -metadata)
  volume.fsck           (-tempPath)

Filer-namespace path flags (`-dir`, `-path`, `-locationPrefix`, etc.)
are unaffected; they live in the filer, not on the local FS.

* shell: reuse util.ResolvePath instead of a new helper

util.ResolvePath already does tilde expansion; drop the local
expandHomeDir helper and route every shell call site through it.

weed/shell/command_fs_meta_save.go

@@ -68,7 +68,7 @@ func (c *commandFsMetaSave) Do(args []string, commandEnv *CommandEnv, writer io.
 		return parseErr
 	}
 
-	fileName := *outputFileName
+	fileName := util.ResolvePath(*outputFileName)
 	if fileName == "" {
 		t := time.Now()
 		fileName = fmt.Sprintf("%s-%4d%02d%02d-%02d%02d%02d.meta.gz",