Use kubectl's base64decode template function (added in K8s 1.11) to
decode values in Secrets. Removes external call to `base64` utility on
the host system.
* Use CodeTabs for examples in multiple formats.
* Ensure correct language on code fences.
* Use CodeBlockConfig for examples with filenames, or which need
highlighted content.
The base64 CLI utility has two different short flag arguments for decode
depending on the platform: -D and -d.
Previously, the docs used the -D flag exclusively with the base64 utility.
Luckily, the long form of the flag is the same across platforms: --decode.
All uses of the base64 -D flag have been replaced with --decode.
* website: migrate to new nav-data format
* website: clean up unused intro content
* website: remove deprecated sidebar_title from frontmatter
* website: add react-content to fix global style import issue
