Remove placeholder section page redirects; move more "overview" pages out from dropdowns

[felker]

After #782 and #781, all top-level section titles in the dropdown now link to actual pages, although some are placeholders /redirects:

user-guides/mkdocs.yml

Lines 150 to 154 in 1fd2be6

	# top-level section empty placeholder pages; eventually add content and remove redirects for most (and/or reoganize):
	'machines/index.md': 'index.md'
	'contacting-support/index.md': 'contacting-support/technical-support.md'
	'data-management/index.md': 'data-management/filesystem-and-storage/index.md'
	'account-project-management/index.md': 'account-project-management/MyALCF.md'

And all Machines > Aurora etc. level-2 sections are links to Machine Overview pages

But there are a few other "Overview" type pages that should be renamed to index.md and associated with the dropdown title: