New command "string pad" to pad text to a given width (#7340)

Pads text to a given width, or the maximum width of all inputs.

doc_src/cmds/string-pad.rst

@@ -0,0 +1,50 @@
+string-pad - pad characters before and after string
+===================================================
+
+Synopsis
+--------
+
+.. BEGIN SYNOPSIS
+
+::
+
+    string pad [(-r | --right)] [(-c | --char) CHAR] [(-w | --width) INTEGER] [STRING...]
+
+.. END SYNOPSIS
+
+Description
+-----------
+
+.. BEGIN DESCRIPTION
+
+``string pad`` pads each STRING with CHAR to the given width.
+
+The default behavior is left padding with spaces and default width is the length of string (hence, no padding).
+
+If ``-r`` or ``--right`` is given, only pad after string.
+
+The ``-c`` or ``--char`` switch causes padding with the character CHAR instead of default whitespace character.
+
+If ``-w`` or ``--width`` is given, pad the string to given width. Width less than the string width will result in an unchanged string.
+
+.. END DESCRIPTION
+
+Examples
+--------
+
+.. BEGIN EXAMPLES
+
+::
+
+    >_ string pad -w 10 -c ' ' 'abc'
+           abc
+
+    >_ string pad --right --width 12 --char=z foo barbaz
+    foozzzzzzzzz
+    barbazzzzzzz
+
+    >_ string pad -w 6 --char=- foo | string pad --right -w 9 --char=-
+    ---foo---
+
+
+.. END EXAMPLES