audio/musicpd: Enable the webdav storage plugin if curl is enabled

Details:

• With curl enabled, the webdav storage plugin can be enabled as well, allowing folks to access their collections via webdav.
• No new dependencies are required to support this feature.

PR: 271663
Reported by: bsd@abinet.ru
MFH: 2023Q2

(cherry picked from commit ca5fd0c991d382e3bcce32dec80dc4c5e6547931)