security/data-protection/configuration updates

[guardrex]

Addresses #3777
Addresses #4534
Addresses aspnet/DataProtection#185
Fixes #3273

Internal Review Topics (Links will be updated when build completes)

index.md
overview.md
default-settings.md
machine-wide-policy.md
non-di-scenarios.md

Note: As usual, API links don't work on the review site. Remove the "review" portion of the domain from the address that comes up in the address bar to see where it goes.

Notes:

• The 2.0 bits were handled back in July
• Mostly a UE/guidelines-adherence pass on this group of topics
  • Dropping anchor links in favor of section headings
  • Links to API topics
  • Conversion to xref links
  • Metadata updates, including title, description, and keyword updates
  • Tables look a lot better (imho) than lists for some of the content
  • Added descriptions on the index page for this group of topics
• Small code updates for the non-DI topic
• Squeeze in a note on addressing Docker ephemeral keys, but I don't think it surfaces well buried in the Key Management topic, so I also add a little blurb at the bottom of the overview topic.
• Did a little more work for Update Key Management Documentation #3273 surfacing the key extensibility topic and key management for web farm scenarios with share access PersistKeysToFileSystem and without share access (use an external provider).

cc/ @ajaybhargavb

[dnfclas]

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