Remove notion of "Advanced Power Settings" in unified KCM

Follow-up to Bug 450276 which advised a merge of "Advanced Power Settings" into the main "Energy Saving" KCM, and that has happened for Plasma 6 so the bug was closed. But it also pointed out the following:

Advanced options go against the Lessons Learned Page: https://community.kde.org/Get_Involved/Design/Lessons_Learned

Tackling this will require more of a redesign than the comparatively tame QML port of what used to be the stand-alone Advanced Power Settings module. The main challenge is that the KCM's main page deals with profiles, so we can't just move the "Other Settings" (Stop media playback when suspending, and Related settings pages) into the main page without causing confusion.

Here are some potential approaches:

a. We could make a fourth tab for misc settings on the main page (e.g. "General"), and rename the "Advanced Power Settings" header action / child page to "Configure Battery Levels" which is what's left if we take out "Other Settings" from that.

b. We could leave the main page unchanged but add "Other settings" (currently just one checkbox and a few KCM link buttons) into hidden-by-default contextual header actions. In other words, get us a "More" [⦙] button and stuff the misc global settings there, then rename the rest to "Configure Battery Levels" like in (a).

c. We could redesign the main page to organize tabs by settings category (e.g. Suspend Session, Display & Brightness, Performance & Scripting) instead of by power state. Lots of discussion has been had at #10, which you're welcome to check out if you want to lose hours, nay, days of your life reading up on all that. Once things are organized by category, it would be easy to find a spot for all global "Other Settings" among the regular profile-aware settings. Like in (a) and (b), we'd keep "Configure Battery Levels" as header action / child page, primarily because it influences profile settings behavior across different categories.