* Clean up of the platform section
This cleans up the platform section into its own subdirectory.
I am not all that happy about how "see-also" works, but maybe that
is how it is meant to work, or alternatively I'm doing it wrong :)
* Apply reviewer comments and add the index file
_index.md was missing from prior commit accidentally.
Removed all "Platform setup for" text in all platform docs.
* Apply reviewer comments
Some wordsmithing.
weight = 3 is intentional to fit alphabet. Assuming nobody
will require ASCIIbetical.
* Fix US English lint errors
* Revert the Chinese translation of the platforms PR
The Chinese language version needs to be ported. This PR
was merged manually which probably has broken the gate.
* Update authentication concept doc.
* Fix lint errors.
* Address comments and fixed some links.
* Remove feature stages change from this PR.
I will make a separate PR for it.
* Consolidate the security concept pages into a single page.
- This updates the security concept material to be on a single page, which matches the
change done last week for the rest of the concept material. This ends up being a less clicky
more directed introduction for newcomers to the platform.
- While I was there, I moved the redundant What is Istio page from our about section and stuck
the content at the top of the What is Istio page in the Concepts section.