Plugins: Inconsistent name in local nav

[fcoveram]

Initially reported here in Learn#2622

"Plugins" is called differently across sections and pages. Here is a table pointing out the places where this occurs.

Menu item in global header	Hero section in Homepage	Section name in local nav
Plugins	Plugins	Plugin Directory

I would change the local nav version to "Plugins" and be consistent with how it works in Patterns