FEATURE: More flexible admin plugin config nav definition (#26254)

This commit changes the API for registering the plugin config
page nav configuration from a server-side to a JS one;
there is no need for it to be server-side.

It also makes some changes to allow for 2 different ways of displaying
navigation for plugin pages, depending on complexity:

* TOP - This is the best mode for simple plugins without a lot of different
  custom configuration pages, and it reuses the grey horizontal nav bar
  already used for admins.
* SIDEBAR - This is better for more complex plugins; likely this won't
  be used in the near future, but it's readily available if needed

There is a new AdminPluginConfigNavManager service too to manage which
plugin the admin is actively viewing, otherwise we would have trouble
hiding the main plugin nav for admins when viewing a single plugin.

docs/CHANGELOG-JAVASCRIPT-PLUGIN-API.md

@@ -7,6 +7,10 @@ in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.30.0] - 2024-03-20
+
+- Added `addAdminPluginConfigurationNav`, which defines a list of links used in the adminPlugins.show page for a specific plugin, and displays them either in an inner sidebar or in a top horizontal nav.
+
 ## [1.29.0] - 2024-03-05
 
 - added `headerButtons` which allows for manipulation of the header butttons. This includes, adding, removing, or modifying the order of buttons.