Change guidance on the use of "username" so that it matches IBM Style and PatternFly recommentations

[IngridT1]

Severity

Minor (cosmetic or small impact)

Priority

P2

Affected page(s)

https://redhat-documentation.github.io/supplementary-style-guide/#user-name

Describe the bug, along with repro steps

IBM used to insist on using "user name" instead of "username", so we have that guidance in the SSG. IBM now says use "username" in new content, and PatternFly recommends "username", so our consoles use "username". We should align the SSG with the new IBM guidance and the existing PatternFly guidelines.

Describe the proposed fix

Change the glossary entry to "username".