docs: fix typos and simplify wording on SSO page

[agilgur5]

Motivation

• Stumbled upon some typos on the page
• Use simpler and more direct language, per the k8s style guide
  • there are (many) more changes that could be made to the docs according to the k8s style guide, but (significantly) limited myself right now to places I'm already applying fixes to 😅
    • didn't want to do wholesale copy-editing of all docs at this point 😅
    • for example, using "you" and avoiding "we", which are switched between many times in the docs. (also, replacing "latin phrases", etc etc)

Modifications

• fix missing spaces, fix missing article ("an", "a")

• use code backticks when referring to a namespace

• simpler + more direct language:

  • "which would allow" -> "that allows" (also prefer present tense)
  • "we will use this to allow" -> "this allows"
  • "that you want to grant to" -> "for"
  • "whenever" -> "when"
  • "we will use this service account to allow" -> "this service account allows"

• reduce repetition

  • "if you wish to" is redundant when it is "optional"
  • "in the namespace" is redundant when it is initially stated that "makes a request in my-namespace"

Verification

n/a