MM-64669 Fix keyboard navigation of settings sidebar (#32098)

* MM-64669 Fix keyboard navigation of settings sidebar and add Playwright test

* MM-64669 Revert changes to Cypress test which masked keyboard bug

The changes that were previously made caused Cypress to refocus the
sidebar repeatedly which stopped the test from failing without fixing
the bug.

* Ensure focus highlight is always visible on sidebar tabs

This may not have been broken by the changes that caused MM-64669, but I
noticed it while I was in there and wanted to fix it.

* Fix settings modal scrolling while changing sections using arrow keys

* Remove accidentally-added field

server/public/model/channel.go

@@ -147,7 +147,6 @@ type ChannelPatch struct {
 	Header           *string            `json:"header"`
 	Purpose          *string            `json:"purpose"`
 	GroupConstrained *bool              `json:"group_constrained"`
-	Type             ChannelType        `json:"type"`
 	BannerInfo       *ChannelBannerInfo `json:"banner_info"`
 }