net-im/telegram-desktop: convert webkit-gtk dependency to OPTIONS (+)

• Add WEBKIT option, disabled by default
• Bump PORTREVISION, default dependencies was changed

Previously dropped GTK option was used to enable gtk native dialogs
and render rich window content.
With last releases WebKit-gtk used only for in-app payments system.
While internal payments still experimental and not wide used,
there is no reason to hook this burden to the build as default yet.

Discussed with: osa, danfe, maintainer via ML
Approved by: maintainer

(cherry picked from commit ece7e7d92c75401608ccb6d64bcdb0b51898fe2c)