Add clarity to transport auth section, inc new mode param (#4356)
Add clarity to transport auth section, inc new mode param (#4356)

* Add clarity to transport auth section, inc new mode param

Arguably the wording here before was incorrect, because the mtls
parameter does have an argument, the mode parameter. This documents
STRICT and PERMISSIVE modes, as well as discussing the equivalence
between STRICT mode and omission of the mode key. It also adds clarity
as to what happens when the section is omitted.

* Fix typos

* Reword omission of tls mode for clarity

* Link to reference docs with equivalence tip

* Remove speculative paragraph

* Link directly to mtls modes reference

* Unbreak line to fix html

* Remove list inside tip

This seems to cause issues with html generation from Hugo

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