Add “conf” wrap preset: toolbar button + default styling for configuration blocks

[VitisEK]

What & why

This PR adds a dedicated conf wrap preset intended for configuration / CLI snippets:

• Adds an editor toolbar button (with icon) that inserts <wrap conf>…</wrap> to make authoring easier.
• Adds default styling for .wrap_conf (monospace, light background, border/padding, overflow handling) to improve readability of config blocks.
• Makes the selector apply as .wrap_conf (instead of .dokuwiki .wrap_conf) so the styling is applied consistently in render contexts where the .dokuwiki wrapper may be absent.

Changes

• action.php: new toolbar entry for conf (format) with images/toolbar/conf.png
• images/toolbar/conf.png: new toolbar icon
• style.less: new .wrap_conf styling

Usage example

<WRAP conf>
enable\\
configure terminal\\
..\\
</WRAP>