docs: cleanup code blocks in bullets

[Billy99]

New to Kepler and was trying to follow the documentation to install Kepler for the first time. The
https://sustainable-computing.io/installation/kepler/#deploy-the-prometheus-operator section has several issues. Primarily, some of the code blocks lead with console in the text, new lines are not honored, and the bulleted numbers don't increment.

Fixes in this PR:

• Added pymdownx.superfences to the markdown_extensions: section in mkdocs.yml. This fixed the newlines not honored in the indented code blocks and allowed the build to recognize the code block language identifier (console).
• Added additional spaces to the code blocks in bulleted sections. This indents the code block to the same level as the text and allows the bulleted numbers to increment properly.
• For code blocks, replaced # with a $. To me, # implies root access is required and none of the documented commands require root access. I will change this globally in the docs if this change is acceptable.
• Added admonition to the markdown_extensions: section in mkdocs.yml. When adding things like Note:, with admonition, if !!! note is used instead, it draws a box around the note. See https://squidfunk.github.io/mkdocs-material/reference/admonitions/. I can remove this, or update the docs globally depending on feedback.
• Changed the default language to English. When building and running locally, it defaulted to Chinese. The problem is that only 3 of the pages are translated into Chinese so it looked like it was in English except for those 3 pages on the table of content. So took a while to figure out that the language for the whole website was set to Chinese and that there wasn't some other issue.

[Billy99]

$ causes a lint error so I removed them.
MD014/commands-show-output Dollar signs used before commands without showing output
See: https://github.com/updownpress/markdown-lint/blob/master/rules/014-commands-show-output.md

[Billy99]

Since @rootfs approved the original commit, made the following additional changes globally:

• Globally updated >Notes: to !!! notes as done in original commit.
• Globally removed # that were in code blocks that didn't require root access.
• Globally indented code blocks in bullet items so the code block matched up with the bullet text.
• Changed all kepler to Kepler were applicable.
• Fixed typos or bad grammer as they were stumbled upon.
• In docs/design/kepler-energy-sources.md, rearranged some of the text to help it read better. Same text, just different order.
• In lines I was already changing for other reasons, it the line was too long, broke it up over several lines.
• Headings should be capitalized. I didn't change every instance, but in some of the places I was already making changes, I updated some of the heading capitalization.
• In docs/design/metrics.md, I fixed the spacing around each counter. Now the text is on a separate line from the counter name.