Gnus: add gnus-summary-browse-url binding

[ttybitnik]

Function: gnus-summary-browse-url
Default binding: 'w'
Proposed binding: 'gX'
Rationale: This same Vim-like binding already exists in the package, but only for the article-mode/map. This addition enables a more dynamic workflow allowing users to open articles' URLs directly from summary-mode, as ̶G̶o̶d̶ ̶i̶n̶t̶e̶n̶d̶e̶d̶ the function name describes.

For the record, I personally have overridden this and other bindings in this module to match the Gnus defaults in my configuration, some of them create less friction IMO. However, I believe I will eventually get used to the choices made by the collection, coming from a Gnus/Emacs defaults background. The more I learn Vim and consider the collections' changes/choices for Gnus, the more they make sense 😄 (Anyways, I digress).

[condy0919]

For the record, I personally have overridden this and other bindings in this module to match the Gnus defaults in my configuration, some of them create less friction IMO. However, I believe I will eventually get used to the choices made by the collection, coming from a Gnus/Emacs defaults background. The more I learn Vim and consider the collections' changes/choices for Gnus, the more they make sense 😄 (Anyways, I digress).

The GNUS bindings are modeled after mu4e's. If you thought it's inconvenient, feel free to open a discussion/PR. 😃