Fix 'Highlighting code blocks in docs '(#5805)

* Fix typo in docs/common.

* Add the Code blocks in the Markdown spec to make docs/common at root easy to read.
Signed-off-by: NydFu <ader.ydfu@gmail.com>

Error in config options re: loopback only versus all interfaces.

* Set default login mode to first authentication-mode option

authentication-mode options specified in backend, i.e. `token` (default),
`basic` or both, are retrieved from frontend, and login mode selections
are set in order of the options specified.

But `Kubeconfig` is set as default in frontend for now.

This commit enables to set default selection by operator's specification
of authentication-mode.

* Simplify logic

* Fix test
Co-authored-by: NSebastian Florek <s.florek91@gmail.com>

Signed-off-by: NBhavin Gandhi <bhavin7392@gmail.com>

Also, cleanup descriptions for `dashboard --help`.

* Add architecture doc
Move images to the new dir

* Add deps managment doc

* Update some of the docs

* Update link to the docs

* Add links to the wiki

* Update 1.6.x-and-below.md

* Update 1.7.x-and-above.md

* Update architecture.md

To migrate wiki contents into `docs/`, prepare directory and file structures.
Contents of each pages would be added as latest in subsequent PRs.