Amazon MSK (Zilla Plus) docs polish

[vordimous]

Updates for content clarity. Reviewing the rendered pages will be beneficial since much of the changes were moving or reformatting the content. live version: https://vordimous.github.io/zilla-docs/next/how-tos/amazon-msk/public-proxy.html

fixes https://github.com/aklivity/zilla-docs/issues/71

[vordimous]

check:

• After logging in via SSH, check the status of the msk-proxy system service.